Micromorphology of an involucral bract and cypselae of the endemic and relict species Amphoricarpos elegans Albov (Asteraceae, Cardueae) from the Caucasus

Abstract

In this study, micromorphology of an involucral bract and inner and outer dimorphic cypselae of the relict Amphoricarpos elegans, endemic from western Caucasus, is examined using a scanning electron microscope (SEM) and presented here for the first time. The middle involucral bract is nearly glabrous, with a reticulate-rugulose surface and an oblong-obtusate mucro. Both cypselae exhibit similar features, viz., narrowly oblong-cylindrical or obovate shape with more or less conspicuous longitudinal ribs, an adaxial detachment area, an asymmetrical carpopodium, absence of a pericarp crown and a barbate-aristate pappus made up of narrow, subulate, basally smooth and apically barbate bristles. However, some differences are evident. The outer cypsela is glabrescent and flattened, with an obscure outline of epidermal cells lacking an end wall and with a sunken periclinal surface and striatereticulate structure. Also, the outer cypsela has two entire, narrow, lateral wings, rounded above; and less numerous pappus bristles in one row. In contrast to this, the inner cypsela has a distinct outline of the epidermal cells, which are rod-shaped with a short acute end wall, a swollen periclinal surface and reticulate structure. The pappus of the inner cypsela possesses many more bristles organised in two rows (a biseriate pappus). Also, slightly pentagonal or round nectary remnants are found in the centre of the upper part of the inner cypsela. The taxonomic value of the analysed characters is briefly discussed.