Aspleniaceae

Abstract

The Aspleniaceae, or family of spleenworts, in the order of Polypodiales or Aspleniales, is a family of fern, consisting of 2 genera, Asplenium Linn. and Hymenasplenium Hayata, with approximately 700 species, subcosmopolitan, but mainly in tropical and subtropical regions. Plants are small to medium-sized, predominantly epilithic or terrestrial, but also many epiphytic. Rhizome is creeping, ascending, or erect, densely scaly. Scales are narrowly lanceolate. Fronds are remote or approximate or fascicled, herbaceous or succulent or subleathery, glabrous or sparsely scaly. Stipes are inarticulate. Lamina are variably shaped, simple or deeply lobed or 1–3-pinnate, apical pinnae usually reduced and confluent into a pinnatifid apex. Rachis structure is variable, adaxially often sulcate, with or without central supravascular ridge, and with or without lateral wings derived from decurrent frond margins. Pinnae and other divisions are often more strongly developed in direction of apex, ultimate pinnules or segments often rhombic, trapeziform, or cuneiform with asymmetrical base. Veins are free or occasionally confluent, with veinlets not reaching margin. Indusia are thinly membranous to thick and firm, usually flat but occasionally rolling back at maturity, free margin entire to erose, sinuate, fimbriate, and glandular. Sporangia are with a vertical annulus of about 20 thickened cells, stalk uniseriate, not glandular. Spores are usually 64 per sporangium, bilateral, elliptic to reniform, monolete, exospore smooth, perispores elaborate and very variable, consisting of three layers. Two species, belong to Asplenium Linn. genus, are illustrated in the chapter.