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Trichome micromorphology in Alcea L. and allied genera (Malvaceae) and its systematic

Citation

Arab Ameri, Mahnaz; Khodayari, Hamed; Zarre, Shahin (2020), Trichome micromorphology in Alcea L. and allied genera (Malvaceae) and its systematic, Dryad, Dataset, https://doi.org/10.5061/dryad.tdz08kpww

Abstract

Trichomes of 26 species of the genus Alcea were investigated using light (LM) and scanning electron microscopy (SEM). The trichomes show a great micromorphological variation, which provides interesting data for species delimitation in Alcea. Two basic types of trichomes can be distinguished in the genus Alcea and the allied genera: glandular and eglandular. The glandular trichomes can in turn be subdivided into two subtypes: capitate and clavate. The eglandular trichomes can be subdivided into five subtypes: simple, fascicled, stellate, fascicled-stellate and pluri-radiate. Characters of taxonomic interest are: trichome density (glabrous to dense), number of arms per trichome, orientation relative to the epidermal surface (appressed to erect) and presence/absence of stalk. According to our results the species of Alcea can be divided into four informal groups based on trichome types. Our results support the exclusion of annual Althaea from the perennial ones and its close placement to Malva. In addition, the close relationship between perennial Althaea and basal Alcea lineages is supported by our trichome micro-morphological investigation. Based on the evolutionary framework provided by recent molecular phylogenetic investigations, following trends can be proposed in Malva alliance: long and narrowly armed trichomes are primitive against the short and thickly armed trichomes, dense indumentum coverage is primitive against the moderately dense or glabrous ones, the presence of simple hairs on stem (particularly on leaves) is more advanced against their absence, spreading villous-stellate and fascicled trichomes are more advanced against the appressed stellate ones and clavate trichomes, which were found exclusively in few species of Alcea, should be considered as a derived state against the capitate ones, and potentially provide a synapomorphy for the crown group of Alcea, but this conclusion needs to be tested by adding more species to trichome morphological analysis.