Leaf Architecture Of Genus Camellia And Its Taxonomic Significance

Camellia L. is the largest but relatively original genus in family Theaceae. The taxonomic treatments of the genus Camellia are still bitterly controversial in classifications of subgenera, sections or species. There are three taxonomic treatments of the genus Camellia frequently referred to in Camellia literatures:Sealy's treatment, Chang's treatment and Ming's treatment, but these treatments are still controversial. Therefore, there still are significant to further study the taxonomic problem of genus Camellia. "leaf architecture" denote the placement and form of those elements constituting the out- ward expression of leaf structure, including venation pattern, marginal configuration, leaf shape, gland position and so on. This term is appropriate because the elements of leaves are organized into certain definite structural patterns capable of description, thus conforming to the definition of architecture as "formation or construction whether the result of conscious act or of growth or of random disposition of parts. Leaf architectural characteristics of 16 sections,137 taxa from genus Camellia were examined to discuss the evolution route and the systematic positions of some species within this genus in order to investigate interspecific variations which are useful in species taxonomic treatment.Our results are as follows:1. Genus Camellia has a common set of traits, is a more natural groups. Leave shapes are symmetric and leave margins has regular spcing.Venations of leaf in genus Camellia are all brochidodromous and camp todromus; there are little differences among the primary veins; tertiary veins are usually reticulate; the margin ultimate venation are forming into a loop or incomp lete; areoles are not uniform in shape and incomp lete or imperfect in system development. There are also distinctive characteristics, which can be used to identify species. They are different in leaf size. The length of leaf is most 5-10 cm, a few up to 15 cm larger, or smaller less than 2 cm. Although many changes exist in leaf shape, briefly, there are 5 basic types, namely, lanceolate, ovate, oblong, long elliptic and wide elliptic. The remaining types of shapes can be regarded as derived. Leaf apex are long acuminate, short acuminate, actue and even blunt. Leaf base are from the ear-shaped, circular to even the wedg. Most species had toothed margin, and some had half toothed margin or entire margin. Suction side of blade of some species had gland, such as sect. Tuberculata, sect. Longipedicellata and sect. Chrysantha. Margin of some species had gland, such as sect. Stereocarpus, sect. Furfuracea, and sect. Pseudocamellia. Areole of C. sasanqua, C. kwantungensis and C. pilosperma were composed of secondary veins and tertiary veins, and the rest species were composed of tertiary veins and quaternary venation, Veinlet of most species are branched two or three times, and little simple or one branched.2. The leaf characteristics Camellia showed a high degree of stability in the species level. The leaf architecture has a certain significance to identify species. The UPGMA dendrogram resulted that:(1) The current study did not support the combinations of sect. Chrysantha and sect. Archecamellia by Ming and affirmed the monophyly of these two sections. In addition, it also slight suggested that sect. Archecamellia and sect. Longipedicellata should be combined. (2) In Ming's treatment, sect. Luteoflora shared many characteristics with sect. Stereocapus, and he put sect. luteoflora into sect. Stereocapus. However, our leaf architecture study showed sect. luteoflora had closest relationship with sect. Thea. Thus, their exact relationship remains questionable. (3) Some species of sect. Camellia had closer relationship with sect. Furfuracea than relationship inter sect. Camellia, supporting combination of sect. Camellia and sect. Furfuracea. (4) sect. Oleifera and sect. Paracamellia had closest relationship, the mergence of the two sections is quite natural. (5) sect. Thea and sect. Glaberrima made one cluster suggests that Ming's combination of the two species is reasonable. (6) sect. Tuberculata and sect. Pseudocamellia had most prominent common characteristic, supporting mergence of these two sections. (7) Of all 4 species in sect. Eriandria, C. salicifolia and C. lawii made one cluster with sect. Theopsis; however, C. cordifolia and C. wenshanensis had closer relationship with C. pilosperma and two outgroup species, showing the polyphyletic characteristic.3. Species evolute from simple to complex. Leaf shape and the leaf base in the genus Camellia show the evolution of different levels. Two or three times branched veinlet are more complicated than the simple or one branched, and the toothed leaf margin are more complex than entire leaf margin. This study showed that lanceolate leaves, ear-shaped leaf base, simple or one branched and entire leaf margin are original characters. There are too few of its kind, and no widespread species; oblong leaves, wedge-shaped leaf base,2-3 times branches veinlet and serrated leaf margin are evolutional characteristics. These species are most adaptable, and most species widely distributed. Among these four pairs of characters, the latter ones have more powerful in the evolution and had in a secondary position.