Study on seed morphometry of some threatened Western Himalayan orchids

Abstract

Physical seed characteristics of 32 threatened Western Himalayan orchids belonging to 23 genera of 3 subfamilies were studied using light and scanning electron microscopy. The species showed remarkable seed shape variations (fusiform, spathulate, ovoid, filiform) irrespective of their taxonomic position. Epiphytes produced relatively small-sized seeds compared to their terrestrial, lithophytic, or mycoheterotrophic counterparts. Seeds were truncated (length/width < 6.0) in 27 species, and were mostly elongated (length/width = 19.957 ± 1.459) in the orchidoid species Goodyera biflora (Lindl.) Hook.f. The number or size of testa cells was found fairly consistent at the genus level, and their walls were straight, sinuous, or undulate. Periclinal walls possessed vertical or oblique ornamentation in 6 species, which is of taxonomic implication. Embryos were rather tiny and most of the seed space (even >90% in 7 species) was occupied by air. The highest seed to embryo volume ratio was recorded in terrestrial Liparis odorata (Willd.) Lindl. and the lowest in epiphytic Rhynchostylis retusa (L.) Blume, both of which are members of the advanced Epidendroideae. Seed characteristics are important in elucidating taxonomic, phylogenetic, and phytogeographic relationships among different orchid taxa.