Systematics Of The Genera Apios Fabr. And Cochlianthus Benth. (Fabaceae)

The two genera Apios consisting of six species and Cochlianthus consisting of two species, are members of subtribe Erythrininae, tribe Phaseoleae in the Fabaceae. Apios is a eastern Asia and North America disjunct distribution genus. Cochlianthus is distributed in the Himalayan region. These two genera have typically been considered to be very closely related. As no consensus has been reached on how many species in Apios, this genus is needed in aspect of taxonomical revision work. Furthermore, the phylogenetic relationships of both in Apios and between Apios and Cochlianthus are not clear yet, and remain to be studied. In my thesis, the taxonomy on Apios and Cochlianthus was revised, and some problems both in Apios and between these two genera were addressed mainly based on evidences from morphology, leaf epidermal characters, palynology and molecular data. The results were summarized as follows: 1. Morphology On the basis of field work and examination on herbarium specimens, the variation of all the major morphological characters in Apios and Cochlianthus was analyzed and their taxonomic significance was evaluated. The tuberose, the shape of leaflet, the florescence and the petal are stable within species and thus are the reliable characters of classification. Based on the florescence of Apios, which may reflect the relationships between species among this genus, we presumed that in Apios, A. carnea could be the advanced species and A. delavayi and A. gracillima be the primitive. 2. Leaf epidermal features The leaf epidermis of all 8 species of Apios and Cochlianthus were examined for the first time under both light microscope and scanning electron microscope. Leaf epidermal characters of these two closely related genera, such as shape of cells, pattern of anticlinal walls, cuticular membrane and wax ornamentation, are usually stable within species and thus of great significance in understanding the relationships between and within genera. The results support that (1) Apios gracillima Dunn should be recognized as a distinct species, not a variety of Apios delavayi Franch.. (2) Subgeneric classification in Apios is not justified. 3. Palynology Pollen of seven species of Apios and Cochlianthus were observed under SEM. All the pollens are tricolporate, circular to oval-triangular in polar view. The pollen of Apios can be divided into two types: the pollen of A. carnea has distinctly reticulate wall; and the other have psilate wall with granulate or short striate ornamentation. The exine type maybe an evidence for the advanced position of A. carnea in Apios. The pollen of Cochlianthus is similar to A. carnea. The pollen pattern may reflect the relationship between species in Apios and Cochlianthus. 4. Molecular systematics Phylogenetic relationships of six species of Apios and Cochlianthus were investigated using maximum parsimony analyses of sequence data from nuclear ITS and H3D. The results strongly support the monophyly of Apios and that the two North American species form a clade, nesting within the clade of the Eastern Asian species. A closely relationship between Apios and Cochlianthus is well supported by our data. The phylogeny trees topology are congruent with some important morphological characters, including the florescence and the pollen. Molecular evidence, as well as the morphological characters, may explain the pattern and possible origin of eastern Asia and eastern North America disjunct distributions in Apios. 5. Taxonomic revision All names of Apios and Cochlianthus ever published are revised. Six species in Apios and two in Cochlianthus are recognized on the basis of above evidences. Five species are excluded from Apios. Moreover, the descriptions,geographical data,keys to species and illustrations of every species in these two genera are given.