Chapter 3

The Evolution of Cultivars

It is not only the basis and prerequisite of scientific classification of cultivars but also an important foundation of cultivar improvement to study the evolutional process of characters of the cultivars and understand their changing rules. Like most horticultural plants, the evolution of tree peony cultivar follows some basal rules but possesses its own traits. Different natural and cultivated conditions, as well as people' s different tastes showing in the process of cultivar selection, may affect even restrict the direction and process of cultivar evolution.

3.1 The Evolution of Flower Color and Blotch

3.1.1 The Evolution of Flower Color

The Pigments Composition of Tree Peony Flower

As an ornamental plant, the flower color of tree peony is the most important character to evaluate a cultivar. The evolution of flower color in nature is a relatively complicated course. The flower color is determined by the composition, content and distribution of the pigments, these three factors are controlled by different genes or gene groups. The flower pigments of tree peony belong to flavone compounds. According to the analysis, there are mainly 6 kinds of anthocyanin pigments, including peonidin 3,5-di-O-glucoside (abbr. as Pn3G5G), peonidin 3-O-glucoside (Pn3G), cyanidin 3,5-di-O-glucoside (Cy3G5G), cyanidin 3-O-glucoside (Cy3G), pelargonidin 3,5-di-O-glucoside (Pg3G5G) and pelargonidin 3-O-glucoside (Pg3G). In which, Pn, Cy and Pg stand for the corresponding aglycone respectively. Besides, there are many other flavones or flavonols compounds, for example the flavones: apigenin (Ap), luteolin (Lu), chrysoeriol (Ch); and the flavonols: kaempferol (Km), quercetin (Qu), isorhamnetin (Is) (Wang L.S. etcd. 2001a; 2001b).

The composition, content and distribution of flower pigments of tree peony are affected by not only the interior genetic factors but also the environmental factors (e.g. light, temperature, the pH and nutrient composition of soil) and other cultivated conditions. During the long period of evolution, as the above factors influenced, the flower color showed obvious difference between cultivars, different areas and cultivar-groups.

The Historical Process of Flower Color Evolution in Tree Peony Firstly, the flower color of tree peony cultivar is associated with that of the original species. Then the flower color has been changing during a long term of cultivation and selection of the new cultivar. The protospecies which had contributed to the formation of the cultivar-group of Chinese tree peony mainly are P. jishanensis (white flower), P. rockii (mainly white, sometimes pink and red), P. ostii (white), and P. qiui (pink). The flower color of these species is simple. With the gene exchange and recombination during cultivation and crossbreeding of intra- or interspecies, the flower color turned to become more complicated. This change of flower color occurred in the Tang Dynasty (AD 618-917) and in the Song Dynasty (AD 960-1279) the bicolor-flowered cultivar (such as ' Erse Hong') and the green cultivar (such as ' Oubi') appeared. From the Ming Dynasty (AD 1368-1644), the transitional flower colors have been found continuously along with the development of cultivation technique and the improvement of environmental conditions. Later some other changes appeared such as white stripes or actinomorphic wirelike stripes on petals. Table 3-1 showed the cultivars grouped by flower color in the past dynasties. The current cultivars of tree peony basically formed nine major groups, namely red, yellow, white, pink, purple, black, blue, green and versi color flowered groups. Each group is further differentiated into different similar colors and transitional colors. For instance, there are peachblow, kermesinus, incarnadine, mauve subgroups in red-flowered group; whiteness and pinkish-white subgroups in white-flowered group; yellowy and golden color subgroups in yellow-flowered group etc. There are no pure red-, yellow-, green- flowered cultivars in Chinese tree peonies, however, the European countries, the United States and Japan have produced the cultivars with pure color flowers through distant crossbreeding and directional selection. Here the application of P. lutea and P. delavayi of China played a crucial role.

The Difference of Pigments between Protospecies and Culti-var-Group

According to the detailed analysis of the flower pigment composition of tree peony, it indicated that different species and cultivars (groups) from different origins (including the species source and the producing area) have different pattern of pigments. And the diversity of pigments also exists among the cultivars of different flower color (Wang L.S. etal 1999, 1998).

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Table3-1 The cultivars of tree peony in the past dynasties of China grouped by flower color (Li J.J., 2002)

Note: (1) The colors are tabulated according to the anth-ographies in the past dynasties. Here peachblow and black have been separated since the Ming Dynasty, "versi color "was added by author, and the "Others "are those colors which are not recorded in the antho-graphies and difficult to distinguish in terms of the cultivar names. (2) In the row below the dynasties, "Count"is the total of the cultivars with corresponding color, "New "is the total of new cultivars in each dynasty.

The Flower Pigments Composition of Wild Tree Peony

Species It showed that there is a big diversity in the composition of tree peony's flower pigments. In the Subsection Vaginatae, the pigments of P. jishanensis are mainly Pn3G5G (82%, the concentration percentage), and the second is Pg3G5G (13%), additionally a little Cy3G5G. P. decomposita is similar to P. jishanensis, but Pn3G5G is 97% in the former. More than half of the pigments in P. rockii' s petals is Pn3G5G (58%), others are Cy3G (42%), a dram of Pn3G and Cy3G5G; while the pigments of blotches at the base of P. rockii' s petals are mainly Cy3G (65%), and others are Pn3G (21%), Pn3G5G (10%) and Cy3G5G (4%). In the Subsection Delavayanae, the flower pigments of P. delavayi consist of Pn3G5G (55%-86%), Cy3G (6%-15%) and Pn3G, Cy3G5G (respectively 11%-16%). P. potaninii' s flower pigments are mainly Cy3G (50%), then Pn3G5G and Cy3G5G (respectively 20%, 21%), the last is Pn3G (9%). The anthocyanin of P. lutea's petals contains only Pn3G5G, while their blotches mainly contain Pn3G5G (52%), others are Cy3G (21%), Cy3G5G and Pn3G. The species P. potaninii var. trollioides with pure yellow flower only has a dram of Pn3G5G and Pn3G (Wang L. S. etal. 2001b).

The Comparison of Flower Pigments between Cultivar-groups There are distinct differences of the flower pigments between Zhongyuan cultivar-group and Japanese cultivar-group, especially in red-flowered cultivars. Japanese tree peony' s pigments are mainly Pg-based then Pn-based pigments. For example, in ' Hohki',' Shin Shima no Kagayaki' and ' Kaoh', Pg3G5G (red) or Pg3G (vivid red) are major pigments, but Zhongyuan cultivars mainly contain Pn- or Pg-based pigments. In the glyco-side level, Japanese tree peonies belong to the balanced type of 3G5G and 3G, namely the content of 3G-type pigments is relatively higher. However Zhongyuan tree peonies have mainly 3G5G-type pigments, then 3G-type, a little of Cy3G, and neglectable Pg3G. In pink-flowered cultivars, the content of 3G-type pigments in Japanese tree peonies is evidently higher than that of Zhongyuan cultivars but other traits are same. Except for a few cultivars, the pigments of the purple-flowered cultivars are almost same too. Generally speaking, there are more red-flowered cultivars in Japanese cultivar-group, but more reddish-purple cultivars in Zhongyuan cultivar-group of China. Pg3G (presenting vivid red) content is very low (<2%) in flowers of Zhongyuan cultivars, therefore it is hard to find the vivid red-flowered cultivars (Wang L.S. et al. 2001a).

The flower pigments are also obvious different between Xibei cultivar-group and Zhongyuan cultivar-group. In Xibei group, several cultivars such as ' Fenjinyu', ' Fen Yanjiao',' Lan Xiannii', the anthocyanin composition of which is PnPg type in non-blotchy part of petals; the flavone/flavonol is mainly Ap, Km type with less Is, namely three kinds coexist. The anthocyanin of most cultivar's non-blotchy part of petal is PnCy type, and the flavone and flavonol consists of Ap, Lu, Ch, Km, Qu and Is, namely six kinds coexist (L. S. Wang et al. 2004). The non-blotchy part in petal of 'Ning yuan Fen' in Xibei group has the equal content of Pn- and Pg-based pigments with less Cy-based pigment, all of which are 3G5G-type. In the brown blotch part, the contents of Pn- and Cy-based pigments are approximately equal, but Pg is lower and Cy-based pigment is higher, Cy3G' s content is high, too. As to the glycoside level, firstly, the pigments in Xibei cultivar flower are Pn3g5G, Cy3G5G, Cy3G, very little Pn3G, and lack of Pg-based pigments. It is the main reason of absence of vivid red and bright pink flowered cultivars in this group. Secondly, in Xibei group, the content of Cy-based pigments is high. Pn3G5G is main anthocyanin, and Cy3G5G is next in the non-blotchy part of petal. In the blotchy part, the brown-red is mainly Pn-based pigments, while the black is Cy-based pigments mainly. Furthermore, the contents of Cy3G and Cy3G5G are approximately equal, but sometimes the later is less in some cultivars. Thus the monoglucosylation or diglucosylation, high content of Cy and its synthesis at petal' s base, attributed the special trait of purple blotch to Xibei tree peonies.

Yan' an tree peony also has its own traits in the composition of pigments. Basically there are 3 kinds: One is the colored but without blotch cultivars, which contain mainly Pn3G5G and little Cy3G5G; the second is the white-flowered but without blotch cultivars, which contain only Pn3G5G; third, the cultivars

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with blotch, the pigments of which are mainly Pn3G5G, the next is Cy3G5G. Here, those cultivars with blotch can be further divided into two parts, namely with 3G-type pigments and without 3G-type pigments. The former contain higher Cy3G in the blotch and have not Pg-based pigments which are also not found in the Xibei cultivars. In which, some cultivars with blotch and 3G-type pigments have similar pigment composition with ' Yeguangbei' and' Honglian' of Xibei tree peony (Wang L.S. 1999).

3.1.2 The Evolution of Blotch

The cultivars with blotch at the petal base are mainly evolved from P. rockii. The blotch has become the main feature of Xibei cultivar-group. For the wild P. rockii, the blotches are mostly black and also some purplish-red ones are found in Shennongjia, Hubei Province. In the cultivars, the black, darkish-purple, brown-red and purplish-red blotches have been observed. These blotches have showed a trend of obviously becoming large in the new cultivars. The outer petal's blotch in some cultivars can take up almost 1/3-1/2 of a whole petal (e.g. 'Mochi Yanxia'). The pigments of blotch in the cultivar-groups of Xibei and Yan'an have been briefly introduced above. According to Wang L.S.' s analysis (2000, unpublished), their pigment composition is similar to that of P. delavayi of the Subsection Delavayanae. As P. rockii directly or indirectly participated in the formation of Zhongyuan cultivar-group and other cultivar-group, naturally more or less blotches at the petal base with different sizes and colors appeared in these cultivars. However, the blotches are generally far less bright than those of Xibei cultivars. Such cultivars take up about 30% in Zhongyuan group and higher rate in Xinan group. In Jiangnan group, the original cultivars with blotch are seldom seen, but the new cultivars with blotch are increasing in Yancheng of Jiangsu and Shanghai in recent years. In addition, in the yellow-flowered cultivars bred abroad, the blotched cultivars also have been found such as 'Le Esperance' etc., which should be associated with P. lutea var. brunnea.

3.2 The Evolution of Floral Organs

3.2.1 The Evolutional Process of Perianth

The Increase of Asexual Petal

The perianth is composed of calyces and petals. It has experienced a variety of changes during the process of long period cultivation and continual hybridization and selection. In which, the increase of asexual petal is one of the most important changes. The layers of petals have increased from 2 of original species to 8-10 of the double cultivars. These petals array closely and trimly on the torus, they have similar shape and turn smaller gradually from outside toward inside. The increase of asexual petals resulted in the formation of hundred-petal flower. The higher the extent of evolution is, the more the petals are.

According to the data of the flower bud differentiation (Wang Z.Z. et al. 1991, 1987) and the author's observation in recent years, the increasing number of the asexual petals is limited. The single form cultivars generally have 15 asexual petals, while the lotus form or crown form cultivars have 30 or so. For some cultivars with an appearance of chrysanthemum form

or rose form, the inside petals array trimly but actually derive from the transformation of stamens. In another case, several layers of outside petals consist of asexual petals, some of which are petaloids (sexual petals) coming from stamens.

The Petalody of the Calyx

Another evolutional trend of the perianth is the calyx's. petalody. In this case, such calyx is called "exterior-colored petals". Most cultivars have 2-3 exterior-colored petals, however a few cultivars have 4-5 or more. This kind of petals can increase the ornamental value at the beginning of flowering.

3.2.2 The Evolutional Process of the Stamen

The variation of tree peony ' s stamen especially the petalody is an important cause of diversity of tree peony flowers. The stamen ' s evolution could be described as several cases as follows.

The Enlargement of the Stamen

The anthers ' enlargement and the filaments ' lengthening and widening make the center of flower vivid golden yellow. At this time the flower form could be called"golden-stamen form" (Fig.3-1,3-2).

The Petalody of the Stamen

There are three cases of stamens transforming into petals:

The Centrifugal Petalody The order of stamens ' petalody is from the inside to the outside, it is consistent with the primary developing direction of stamens and opposite to the exterior asexual petals ' increasing direction (Fig.3-3). Such petals usually exist in clusters (mostly 6 clusters, one of which is smaller). These petals are adequately petaloids, large body, and getting smaller gradually from inside to outside. Some filaments of stamens turn petaloids at one side or both sides, but they remain either anthers or some stamens among the petaloids. The center of the whole flower protrudes to become the crown forms.

The Centripetal Petalody The petalody order of the stamens is from outside to inside in this case. There is distinct difference in size between the petals from the stamens petalody and the exterior asexual petals (Fig. 3-4), but there are also some petals difficult to distinguish. At the flower center of these cultivars, there are usually normal stamens and pistils, which form the "heart of exposure", somebody called it "golden-heart form" (Gao Z.M. et al. 1996). According to the author ' s observation, in these cultivars, some are only partially petaloids at the edges of stamens (e.g. 'Chen Hong ' of Zhongyuan cultivar-group), some are the intermediate forms during the transformation of single form to crown form (e.g. 'Honglou Huijin ' of Xibei cultivar-group).

The Irregular Petalody In this case, the petalody of stamens has no rules to follow, namely the stamens ' petalody occurs to different extent, moreover, and a number of normal stamens still remain among the stamen-petaloid petals.

The Increase, Decrease, Degeneration and Extinction of Stamen

Extreme Increase in the Quantity of Stamen This situation generally occurs in the traditional cultivars in the Xinan regions and the Jiangnan (Table 3-2, Table 3-3). In some of the rose form

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Figure 3-1 Golden-stamen form

Figure 3-2 Golden-stamen form

Figure 3-3 The petalody or degeneration process of tree peony 's stamens

Figure 3-4 The golden-heart form

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Figure 3-5 The increase of carpel's quantity of 'Shibahao '

cultivars, the number of the stamens is up to 700; some of proliferation form cultivars even have up to 1,200 stamens. In the some new cultivars produced in Baokang, Hubei, the stamen's number is over 500 (e.g. 'Fendie Xianjin').

Extreme Decrease and Degeneration even Extinction of the Stamen This situation is usually seen in Xibei cultivar-group. In some cultivars with single form or lotus form flower, only a few stamens remain in the flower' s center (e.g. ' Yeguangbei',' Honghai Yinzhen'). Some cultivars have no stamens or only remain acerose vestige.

3.2.3 The Pistil's Evolutional Process

The pistil' s evolution plays a part in the flower form formation of tree peony, especially affects the proliferation form obviously. The pistil' s evolution could be summarized as follows.

The Increase of the Carpels

It is generally seen in all cultivar-groups. In the Subsection Vaginatae, all ancestral species have 5 carpels, but in the cultivars the carpels are mostly over 5. For example,'Zi Erqiao' (viz. ' Luoyang Hong') and ' Shibahao', which are commonly seen in

Zhongyuan cultivar-group, have up to 19 carpels, 2-3 layers (Fig. 3-5). The outer pistils are obviously larger than the inner ones. Recently, it is found that the increase of the stamens usually accompany with the increase of the carpels in some hybrids of interspecies when investigating the tree peonies of Baokang in the west of Hubei (Table 3-2).

The Carpel's Petalody

The carpels become the petalody in various degrees as their number increase. The green or colored petals formed by the pistil' s petalody are called "the inner colored petals", which are thick and usually have floss at the dorsal sutures or remain stigma' s vestige at the dorsal sutures of the median or upside of the petals. These colored petals usually have the vestige of disc (e.g. little fragment, small tubercle or stamen-petaloid structure) and are easily distinguished from stamen-petaloid petals. These petals usually make the flower color more diversified.

The Heteromorphic Development of the Carpel

This phenomenon was found during investigating the development process of the proliferation form flower of tree peonies. It suggested that the upper-flower of proliferation form are formed by the carpel's heteromorphic development (3.3, Chapter 3).

The Degeneration of Pistil

It is hard to see degeneration, decrease even extinction of pistils in the single tree peony. However it is commonly seen in the upper flower of proliferation form tree peony.

3.2.4 Others

The majority of the existing cultivars have one flower in one branch, but the situation of two or more flowers in one branch is found in a few cultivars such as 'Shuanghua Bai'and 'Yanwei Bai' of Xibei cultivar-group. ' Kaoh', a Japanese tree peony cultivar, is also seen two flowers in one branch (Fig.3-6). It is possible the expression of ancestral trait of tree peony, namely more flowers per branch.

Table3-2 The flower constituents of some tree peonies in Baokang

Note:In the column of "Petals", the data in the brackets represent the number of the middle, small petals.

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Figure 3-6 Two Flowers in One Branch in 'Kaoh '

Figure 3-7 Proliferation flowers 'Luoyang Hong '(up), 'Shanhutai '(down)

3.3 The Formation and Evolution of the Proliferation Flower

3.3.1 The General Introduction of the Studies on Proliferation Flower

Overlapping of two or more flowers forms a proliferation flower, which is commonly seen in the highly-double cultivars of the tree and herbaceous peonies. This phenomenon also occurs in other ornamental plants such as plum blossom (Primus mume), lotus (Nelumbo nucifera) etc.

Overlapping of flowers generally forms two layersfoccasionally three or more layers). The upper single flower (or two flowers) is usually called "the upper-flower"; the lower single flower is called" the lower-flower". Basically, the evolutional extent of the lower-flower represents the evolutional trend of the whole proliferation form flower.

In the Bei Song Dynasty, the proliferation form flower was recorded in the florilegium of peony. In 1932, B. Miyazawa reported the proliferation form phenomenon in the Japanese herbaceous peony cultivars. In 1960, Li J.J. preliminarily discussed the proliferation form phenomenon when he investigated the peony cultivars of Heze, Shandong. * [*Li J.J. etc. 1960.Tree and Herbaceous Peonies in Heze.Shandong. Mimeograph,Beijing Forestry College] In 1962, Zhou J.Q. divided the proliferation form flower into the hundred-proliferation and crown-proliferation forms in terms of the lower-flower's feature. Later, according to the evolutional process from the lower to the advanced, Qin K.J. (1987) divided it into 4 flower forms, namely primary-proliferation, colored petal proliferation, delaminated-proliferation and globular-proliferation flower. In 1995, based on the quantity analysis

of the herbaceous peony, Liu C.Y. and Wang L.Y. considered that most of the single forms have a possibility to transform into the proliferation form flower. Except the single form and the golden-stamen form, each single form has the corresponding proliferation form. There are totally 7 kinds of proliferation form. Then Wang L.Y. (1997) also used this result in the classification system of tree peony cultivars.

Recently, Professor Lian Y.S. of Northwest Normal University and the author found that the peony' s proliferation form flowers resulted from the continuous differentiation and hetero-morphic development of the single flower's carpels through observing and analyzing the peony' s proliferation form flowers (Lian Y.S. et al. 2004). This is a significant scientific breakthrough

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Figure 3-8 Organic morphology of the upper-flower of the proliferation form in tree peony (Lian Y.S. 2004).

(1) The calyces with tomenta, abnormal stigma and disc;

(2) The petals with tomenta;

(3) The petals with abnormal stigma;

(4) The anthers with ovule and abnormal carpel;

(5) The complex structure of ovary and anther.

Figure 3-9 The upper-flower 's layered structure of proliferation form flower of tree peony

(A) The upper-flower of the proliferation form of Wuzhou Hong 'in Zhongyuan group;

(B) The upper-flower's layered structure:

(1) Five carpels of the lower-flower;

(2) The sepalody of carpels in the upper-flower;

(3) The petals of the upper-flower;

(4) The carpel-petal complex structure in the upper-flower;

(5) The stamens-ana carpels in the upper-flower.

in the theoretical study in the formative cause of the peony's proliferation form flowers.

3.3.2 The Formative Cause of the Proliferation Flower in Peony

The Origin of the Proliferation Flower

During investigating a variety of double cultivars, we found the following phenomena:

In some highly double cultivars, the number of the carpels increase continuously and then the flower become the proliferation form. The primary single flower cultivars, for example, 'Zi Er qiao' and ' Wuzhou Hong' of Zhongyuan tree peony, ' Kaoh' of Japanese tree peony, all could be seen coexistence of the single and the proliferation form flower (Fig.3-7). Apparently the formation of proliferation form flower is directly correlated with the quantity of carpellary primordium.

In the upper-flower of the proliferation form, the calyces and the petals of outermost layer often have the remaining vestige of stigma and have relatively distinct transitional morphology and colored stripe. Furthermore, most of which are two-side folded and the folding degree decreases gradually along with the increase of the sepalody and petalody level. Some stamens expand at the base and have the similar morphological character of the carpel (Fig.3-8).

As a mark trait of tree peony' s carpel (except the glabrous species or varieties), the tomenta often appeared on the calyces and outer layer petals at the primary phase of the upper-flower's transformation. It even could be seen in the filaments or anthers of some stamen in the process of transformation.

Unlike the lower-flower, the carpels of the upper-flower of proliferation form increased in quantity and the number is variable. The carpels outside are bigger than those inside, the carpellary primordia in the center often undergo the continuous differentiation.

In the upper-flower, strongly unsymmetric development appears in calyces, petals even stamens. When one side fully opens and appears the feature of the transformed organs, the other side

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Table 3-3 The structural comparison of floral organs in the proliferation form cultivars of tree peony

*The number of column "Petals " is a total of big, medium and small petals.

still remains the tomentose trait of carpels.

The gynandromorphism (combining the carpel' s trait of ovule and tomenta and the anther structure of stamen) or carpel-petal mosaic (with both the carpel' s trait of ovule and tomenta and the primary petal) are commonly seen in the upper-flower of the proliferation form.

In addition to the phenomena above, many evidences in anatomy suggest that the structures of the upper-flower in the proliferation form, such as calyces, petals and stamens, have a close relationship with carpels. Therefore, it is concluded that the proliferation form flower resulted from the sharp increase of carpellary primordia and homologous heteromorphosis development (Lian Y.S. et al. 2004). The formation of the proliferation form flower must meet two basic conditions as follows: firstly, the center of the flower can form a number of carpellary primordia; secondly, these carpellary primordia can respectively and successively develop into calyces, petals and stamens etc. (Fig.3-9).

The Heteromorphic Development Process of Carpellary Pri-mordium in the Formation of Proliferation Flower

In the heteromorphic development process of the upper-flower of proliferation form flower, sepalody, petalody and staminody of carpellary primordium happened successively (Zhao M.G. 2002).

During the sepalody process, the carpellary primordium firstly extends breadthwise and transforms into the ovary-like structure,

meanwhile the margin cells at the two sides dedifferentiate and divide into non-carpel tissue cells. This process represents the following traits: firstly the epidermis cells at the edge of two sides lose the trait of tomenta; then non-carpel cell tissue further divide, grow, widen and expand; finally, the folded two sides unwrap and flatten to calyx form as the extinction of the tomenta on the keel. The petalody process of the carpellary primordium is similar to that of its sepalody but ovary-like structure does not appear. The much inner layer seems to transform earlier and more thoroughly.

The staminody of carpellary primordium includes three styles:

1. Linear evolution. The carpellary primordium is filose in the whole evolution process to stamens, or the carpellary primordium' s middle-lower part expands little and appears the similar outline of ovary, while middle-upside part is filose;

2. Ovate evolution. It is the main evolutional manner. As the carpellary primordium' s evolution to stamen began earlier, the transformed primordium has possessed the anther structure and function of real stamen. The stamen's quantity is usually large and some anthers still remain various morphological characters during the transformation process;

3. Mosaic evolution. It is an emergent evolution. The stamen' s lower part still remains ovules while the upper part possesses the anther' s structure and function.

In the upper-flower of the proliferation form, the disc always occurs accompanying with the carpel. When sepalody of the carpellary primordium begins, the disc at the base of the carpellary primordium' s back either degenerates into a small protuberance or

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develops into a small lamellar. When petalody of the carpellary primordium begins, the disc at the petal' s back either forms a small lamellar, a small petal, or develops into stamens, tubular petals or the complex of small petals and stamens.

3.3.3 The Evolutional Traits of the Proliferation Flower of Tree Peony

According to the floral structure analysis of the nationwide proliferation form cultivars (Table 3-3) and the observation of their flowering, we can conclude:

—The flower proliferation phenomenon closely associates with the evolutional level of cultivated cultivar and it appears more frequently in the traditional cultivars. In the cultivar-groups of Xinan and Jiangnan, three-flower proliferation form is seen in a few cultivars, such as ' Yanzhi Lou', ' Xuesi Hong', ' Yu Chonglou', 'Yulouzi'. The quantity of floral organs in which increases extremely. For some cultivars, it is even up to 1,000-1,400 per flower.

—In many cultivars, the heteromorphosis development of the upper-flower's carpels is not complete and their structure is not integrated. In some cultivars, it is only seen the alternate arrangement of big and small layered petals. This kind of proliferation phenomenon is only identified by the size and density of the vascular bundle scar on the receptacle.

—The lower-flower of proliferation form usually differentiates completely. However, because of the difference in the position of flower-bud and the nutrition of branch, the development levels of the proliferation form flowers at different positions in the same plant are largely different. For example, 'Yuhu Bingxin' of Xibei cultivars, its top flower-bud becomes crown-proliferation form, but flower buds of the lateral branches or the lower sites usually form single-proliferation form.

—The form of proliferation-flower is usually unstable, which shows the following two situations: one is that no matter how much is the extent of petalody, it always appears to be the proliferation form flower (e.g. ' Yuhu Bingxin' of Xibei cultivars); the other is that single form and proliferation form flowers coexist in the same plant (e.g. ' Wuzhou Hong',' Shanhu Tai' of Zhongyuan cultivars). Most proliferation form flowers are hardly distinguished from single form flowers by the appearance, especially the proliferation three-flower cultivars, it is necessary to anatomize carefully in order to identify them correctly.

3.4 The Discussion of the Evolutional Rule of the Flower Form

3.4.1 The Basic Evolutional Way of the Flower Form and its Effect on the Cultivar's Traits

The Types and Origins of Petal of Tree Peony

The various flower forms of tree peony are respectively composed of the different original petals and other floral organs. The petal can be classified into two kinds: asexual petal and sexual petal. The asexual petal includes the primitive asexual petal and new-differentiated asexual petal; the sexual petal includes the stamen-petaloid petal, carpel-petaloid petal and tubular petal.

In the sexual petals, the origin of the stamen and carpel-petaloid petals is clear. The tubular petal is only seen in the high-

evolved upper-flower of the proliferation form flower. The coloration style of this kind of petals is contrary to that of the normal petals, namely the outside color of the tubular is deeper than the inside. The tubular petal is the complex product, which integrated the primary cells of carpellary tissue undergone the petalody and backward extension and the petaloid disc tissue (Lian Y.S. et al. 2004). In tree peony, this kind of petals takes up approximately 5% in the upper-flower of the proliferation form flower. According to the anatomical investigation, the primitive asexual petals possibly evolved from the leaf sheath (the degenerate leaf and petiole) (Zhao M.G. et al. 2002), the new-differentiated asexual petals are considered by the majority as a consequence of the natural increase of petal (Zhou J.Q. 1962).

The Basic Evolutional Way of Flower Form

Development of Asexual Petal and Formation of Single Flower The primitive asexual petal is the base of the single flower in Paeonia. Such petals in the protospecies of tree peony may be morphologically divided into two kinds: one is the Subsection Delavayanae, which have the obovate and rectangularly round petals with nearly entire margin or with a cusp; the other is the Subsection Vaginatae, in which the petal is nearly wide elliptical, usually concave on the tip and wide at the base. According to the observation of the petal' s development, in the primitive petal period, the petals are generally three in one whorl. In the maturation period, the petals of the Subsection Delavayanae arrange spirally, but in Subsection Vaginatae, the two whorls of petals turn to one whorl, one petal degenerates and the left 5 petals constitute one whorl. Consequently, the two primary flower forms are established: the spiral flower form and the two-whorl flower form (Zhao M.G. 2002). The existing cultivars mostly evolved from the species of the Subsection Vaginatae, so the primary two-whorl flower form belongs to the common single form. The golden-stamen form, which originated from the extension of the stamens of the single form (e.g. 'Meihong Jinrui'of Xibei tree peony), should belong to the single form, too. However this kind of tree peony cultivars is not commonly seen so far.

The Formation and Evolution of the Semi-Double Form and Double Form There are two basic evolutional ways of the primary single form to semi-double form and double form. One is the increase of the asexual petals. On the base of original two-whorl asexual petals, the asexual petals increase continuously to different extent and result in a series of hundred-petal flower forms, such as lotus form, chrysanthemum form and rose form, but centripetal petalody of the stamens occurred in the advanced flower forms. Furthermore, the cultivars with the inner petals consist of sexual petals (stamen-petaloid petals) and a similar appearance of chrysanthemum form or rose form occurred. The other way is the increase of the stamen-petaloid petals. The stamen' s petalody is mainly centrifugally petaloid, in which the following events occur successively:

1. Filaments and anthers become petaloid and transform into the narrow strip petals. The flower form in this period is called "the anemone form";

2. In the flower center, most of stamens occur petaloid and extrude, only a ring of normal stamens remain between the inner and outer petals. This flower is called "the golden-ring form";

3. Most even all stamens become petaloid in the flower center and make the flower extruded, but the outer petals are larger and easily distinguished from the inner petals. This flower is called "the crown form";

4. In the flower center,

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most even all stamens are petaloids, but there is no distinct difference between the inner and outer petals. This flower is called "the globular form". In the later period of the evolution, the pistil' s quantity possibly increase and even all the carpels become petaloid green petals, namely these petals form a "green heart" usually called "Cha Cui"(green insert). However this flower still belongs to single form before the upper-flower organs occur during the heteromorphosis development of the carpel. The stamens sometimes also have the phenomenon of centripetal petalody and then form "the golden-heart form"flower.

The Evolution of Proliferation Form The proliferation form flower arises from the various single forms because of the rapid increase of carpels and their heteromorphosis development. It is a kind of secondary derivative flower form. The proliferation form still presents the evolutional rule from the lower to the higher level. Qin K.J. (1987) discussed this process in the classification of the proliferation form. Recently, according to the organ structure and evolutional level of the upper-flower of the proliferation form, Lian Y.S. et al. (2004) divided the two-flower proliferation form into the following three forms:

1. Green-proliferation. It is simple and only composed of calyces and pistils. It is named after the green calyces.

2. Gorgeous-proliferation. Except for the calyces and pistils in the upper-flower, a number of petals are well-developed and only sometimes a few filose stamens appear. It is called "gorgeous-proliferation"because of the vivid color of the petals.

3. Golden-proliferation. In the upper-flower, the calyces, petals, pistils and stamens completely differentiated, especially the stamens develop well.

The flower is called "golden-proliferation "which presents the highest evolutional level in the two-flower proliferation. The two-flower proliferation can further evolve into three-flower proliferation with more complicated structure. They are only the basic evolutional patterns of proliferation form flower, the actual status is much more complicated than the discussion above. For hundred-petal and crown sections of the single form, each section possibly form a corresponding proliferation form flower. But so far the observed flowers are mostly double proliferation forms, such as rose-proliferation, crown (colored petal) -proliferation etc. Furthermore, it is found that the layered-proliferation and globular-proliferation evolved from colored petal proliferation.

The Different Petal Types' Effect on the Characteristic of Cultivar Different origin of petals and various structures of flower form have an important effect on the cultivar traits. They affect both the ornamental quality and the flower's adaptability. Generally speaking, the vascular tissue of the asexual petals differentiates completely and these petals are resistant to solarization. On the contrary, the stamen-petaloid petals usually can not resist solarization. It is why many double cultivars of crown section need shade shed during flowering. Of course, the solarization-resistant ability of flower is related to flower color.

3.4.2 The Relationships of the Cultivar Evolution and the Natural and Cultivated Conditions

The evolutional process and degree of the cultivar have a close relationship with natural and cultivated conditions in the producing places. The differentiation of flower color, the composition and vividness of pigments between the cultivar-groups are influenced

by the climate and soil conditions. Some of traditionally long-period cultivated cultivars presented the following evolutional features: First, in the single form cultivars of the hundred-petals flower, petals and stamens increase extremely. Second, the flower organs undergone continuously intense differentiation and the majority of the flowers converted into the proliferation form. This kind of proliferation form cultivars are seen everywhere in the cultivar-groups of Xinan and Jiangnan. Two kinds of cultivars above are all sterile and reproduce only by asexual propagation. The cultivars of Feng Dan series, however, still maintain the traits of numerous flowers, simple flower form and high fruiting rate fructification after a long period of sexual propagation. When it is concerned to the stamen' s evolution, as an obvious contrast to the above cases, only in single form and lotus form cultivars of Xibei tree peonies, it is found that the stamens extremely decrease or even completely disappear.

Generally speaking, the strength of cultivar evolution, especially the rate of the proliferation form cultivars in all cultivars is closely related to the degree of horticultural cultivation in the different places. For example, no proliferation form cultivar is found in more than ten cultivars of Yan' an tree peony and only about 5% are proliferation form in hundreds of Xibei tree peony cultivars. Although there are no more than twenty cultivars in Xinan cultivar-group, the rate of proliferation form cultivars is up to 50% or so.

3.4.3 The Relationship between the Cultivar Evolution and People's Aesthetic Sentiment

As a product of the artificial selection, the formation and development of cultivar is not only affected by the natural conditions also restricted by the aesthetic sentiment and value tropism of the people. Through all the ages, Chinese people are always fond of the double flower cultivars, so the double cultivars take up a higher rate in all cultivars of tree peony. This selective standard formed as early as in the Song Dynasty .There were 24 cultivars recorded in Ou Pu. In which, there were 3 single form cultivars (12.5%), 10 multiple petals cultivars (41.7%) and 11 double flower cultivars (45.8%). In Zhou Pu, 53 cultivars were recorded, no single form cultivars, 2 semi-double cultivars (3.8%) and 51 double flower cultivars (96.2%). During the period of only 40 years from Ou Pu to Zhou Pu, the selection of cultivar is so intense that a variety of variations occurred. The preference for double flower through China has lasted today. However, as an intensive contrast in Japanese tree peony, the majority of Japanese cultivars are the single and semi-double cultivars in hundred-petals section. Only a few of crown section and proliferation form cultivars are found. Apparently, to some extent, it has something with Japanese preference, besides the influence of the climate condition. At present, only the single, semi-double cultivars of Xibei tree peony could present the various blotch patterns, so these cultivars have been paid a considerable attention in the artificial selection.

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next: 4. Cultivar Classification