Guangxi Zhiwu (Oct 2023)
Leaf epidermal micromorphological features of Rhododendron subg. Tsutsusi (Ericaceae) and their taxonomic significance
Abstract
In order to clarify the relationships in Rhododendron subg. Tsutsusi, micromorphological characters of leaf epidermis were examined for 37 species in Rhododendron subg. Tsutsusi using scanning electron microscopy (SEM), among which the relevant features of 29 species are reported for the first time. The results are as follows: (1) The stomatal apparatus are anomocytic and all on abaxial surface. (2) According to the micromorphological features of glands, trichome types and stomatal apparatus of leaf epidermis, subg. Tsutsusi can be divided into five types, i.e., R. simsii-type, R. mariae-type, R. indicum-type, R. saxatile-type and R. farrerae-type. (3) The plants in R. simsii-type have the similar morphological features, have no or discontinuous ringed striates around stomatal apparatus. (4) The plants in R. mariae-type do not have distinct T-pieces at the polar regions of guard cells but have multilayer ringed striates. (5) It is implied that the plants in R. indicum-type have the close affinity with subg. Therorhodion in having distinct T-pieces at the polar regions of guard cells. (6) R. saxatile-type differs from other types in its simple trichomes being virgate but without glands. (7) The leaf epidermis of R. farrerae-type has glands only. (8) The relationships between the closely related species are also discussed on the basis of leaf epidermal micromorphological features. For example, R. hypoblematosum and R. polyraphidoideum tend to be treated as separate species. Support the preservation of R. naamkwanense var. cryptonerve as a variety of R. naamkwanense, and do not support the R. adenanthum into R. tenue as a synonym. The results of this study show that micromorphological features of leaf epidermis are of significant value for species delimitation in subg. Tsutsusi.
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