Comparative Floral Structure of Four New World Allium (Amaryllidaceae) Species

Abstract—

Scanning electron microscopy has allowed the characterization of cell pattern and ornamentation of the bulb coat, leaf, and seed coat, thereby improving and providing consistency to the taxonomy of Allium. However, the pollination biology and taxonomic understanding of Allium is far from complete, in part because floral structures have been investigated in detail for only a few species. Accordingly, this study provides a description and micro- and macromophological comparative analysis of floral characteristics (including the adjacent bulbils of A. geyeri var. tenerum) of four New World Allium species (A. cernuum, A. geyeri var. tenerum, A. stellatum, and A. textile). Observations of fresh material demonstrated that A. geyeri var. tenerum is distinguished from the closely related A. textile by a larger perianth with elliptical tepals (as opposed to ovate to oblong), filaments slightly shorter than tepals (as opposed to 2/3 as long as tepals), and globose young inflorescences (as opposed to ellipsoid). Ridged cuticles from a variety of floral parts have often been reported in Allium as the main type of epidermal cell covering; results from this study indicate that shape and distribution of cuticles are of systematic significance in conjunction with location of the septal nectary opening, development of ovarian processes, and shape of anther apexes. The presence of ovarian processes is considered a recently derived character; we hypothesize that these structures function as non-secretory visual attractants to pollinators, and in concert with broader inner filaments and clearly concave inner tepals may also represent a special adaptation to facilitate retention of abundant nectar secreted in nodding flowers of A. cernuum and in widely spreading flowers of A. stellatum.