Cytological Observations on Asplenium paucivenosum

Abstract

Aspleniunm paucivenosum is very rare in the eastern Himalayas. It prefers wellshaded rock crevices deep in the forests in the Darjeeling district of West Bengal and Sikkim, between 2,400 and 2,700 m altitude. The chief features distinguishing A. paucivenosum from A. dalhousiae are the conspicuously hyaline and chartaceous margin of the pinna lobes, the discrete sori at maturity with well-developed, persistent indusia (which are almost the same size in both species), and the large spores (70-86, X 54-624) with a very broad perispore forming a reticulate pattern of the surface folds. The fronds are 4-30 cm long and 1.5-5 cm wide, with small but distinct, scaly stipes and midribs that are scaly beneath and often wavy; the sinuses between the lobes of the laminae are rounded. Asplenium dalhousiae, which grows in the crevices of rocks or masonry or often in the shade at the base of shrubs between 900 and 2,100 m altitude, has often confluent sori, with the indusium curling back or even deciduous at maturity, and small spores (28-45/, X 24-30,1) with a relatively narrow, folded perispore. Throughout the western Himalayas (Kulu, Simla, Nainital, and Mussoorie) A. dalhousiae is a diploid, with n = 36 (Bir, 1959, 1962b, 1965; Mehra & Bir, 1957). Both tetraploid and octoploid sexual plants of A. paucivenosum have been found in Darjeeling and Sikkim in the eastern Himalayas (Bir, 1960; Bir in Mehra, 1961). These are easily distinguishable in the field on the basis of frond size (Figs. 1A, 2A). Tetraploid plants (n - 72 during meiosis; Fig. 1B), collected only at Tonglu, have small fronds. The octoploid plants (n = 144 during meiosis; Fig. 2B) grow abundantly in Senchal forest near Darjeeling and near Lachen in Sikkim. These are robust, with larger fronds, stomata, epidermal cells, and spores