Micromorphology of endemic Centaurea glaberrima subsp. divergens (Asteraceae)

In this study, the micromorphology of the vegetativeand reproductive structures of the endemic Centaureaglaberrima Tausch subsp. divergens (Vis.) Hayek (Asteraceae), using scanning electron microscope (SEM), ispresented for the first time. Uniseriate whip-like non-glandular and biseriateglandular trichomes are found on the surface of all aboveground parts (stem,leaves, peduncles, involucral bract). On the adaxial leaf epidermis ribbedthickenings (striation pattern) of outer periclinal cell walls, slightly curvedanticlinal cell walls and anomocytic stomata are noticed. Rugose abaxialsurface with thorny protuberances of the involucral bract is documented.Corolla is glabrous with longitudinally parallel epidermal cells with distinctstraight outline. Isopolar, radially symmetric and tricolporate microechinatepollen grains are seen. Short stylar hairs, without cuticular striations, arepresent along the outer sides of the style, while the inner sides (abaxialsurface) constitute the papillate stigmatic surface. Microcharacters found incypsela are as follows: slightly ribbed body; rotund base; lateral and concaveinsertion; short, unicellular curly acute trichomes; smooth epidermis;fine-sulcate ornamentation; rod shaped epidermal cells with short, obtuse endwalls and straight anticlinal walls; poorly developed minutely dentate pericarprim; and dimorphic pappus with bristles of different length and morphology, with pinnulesrestricted to the margins of the bristles. The results obtained contribute toknowledge about the micromorphology of the studied endemic species and providefeatures for its better identification. The taxonomic significance of the analyzedcharacters is discussed. Some well defined microcharacters of the studiedspecies might have taxonomic value.