No abstract

No abstract

SEM examination o f the epidermis o f mature leaves of 37 species in the ten sections ofJatropha (Euphoi-biaceae) has provided information consistent with an earlier revision o f the genus. All species examined show basic paracyic stomata, excluding J . jr~montioides which has anisocvtic \ t~i i i d t~i .Subgenera are well demarcated by presence of true parac!tic \tuniat;i 1 1 1 \uI)gciiii\ ( i ( i ( , o and hrachyparacytic stomata in SubgenusJatropha. The two subgenera can also be distinguished by the presence o f smooth hairs in subgenusJatropha and verrucose hairs in subgenus Curcas (except in wction Curcnxi. Uniseriate, inulticellular hairs occur only in the three most advanced. closely related. sections (Jutropha, Cohucca and Spmosae) in subgenus Jatropha. Similarities and dirsimilarities of cuticular ornamentations, shape of the epidermal and vein cells and direction of antirlinal walls can be used as distinguishing characters, usually significant at thr species level.

Scanning and transmission electron microscopy of pollen grains of 29 species, representing the ten extant genera of Cycadales, has provided valuable insight into their relationships. Pollen grains of these taxa are boat‐shaped, monosulcate, and bilaterally symmetrical. They range from narrowly to widely elliptical or subcircular when viewed distally, and have an exine surface of psilate, foveolate, or fossulate. Pollen wall ultrastructure of Cycadales is typically tectate with alveolate∗∗∗spongy exine. The nexine is laminated in all genera. Nexine 1 (footlayer) is present in most species as a thin and often discontinuous layer. There is consistent variation in thickness of the sporoderm layers among the genera but relative uniformity within them. Pollen characteristics are well correlated with macro‐ and micromorphological features, chromosome numbers, geographical distribution, and postulated pollination mode. A close affinity between Encephalartos, Lepidozamia, and Macrozamia is recognized. Pollen characteristics of the genus Bowenia show some similarity with those of the latter group. Except for two species of Macrozamia which are narrowly elliptic, all of the genera have widely elliptic pollen and share a psilate exine surface and the thinnest sexine with nearly identical arrangement of alveoli. Pollen grains of the species in the genus Dioon exhibit a unique morphology but are more similar to Stangeria than they are to those of taxa in Zamiaceae. The circular outline of the grains and the foveolate exine surface are characters shared by these two genera, but several morphological features distinguish Dioon from Stangeria. Ceratozamia and Zamia share a widely elliptic shape, foveolate exine surface and nearly identical sexine, as well as morphological features and chromosome numbers. They differ from Microcycas in sexine thickness, gross morphology and chromosome numbers. The pollen grains of Cycas circinalis and C. revoluta differ in size and structure of the sexine from all other genera and from each other, substantiating their distinct subgeneric delimitations.

No abstract