Comparative morpho-anatomy of the sporophyte of the most austral American species of Didymoglossum (Polypodiopsida: Hymenophyllaceae)

Didymoglossum (Hymenophyllaceae) is a monophyletic genus that includes small, epiphytic or epilithic plants. Three morphologically very similar species are found in the southern sector of the Yungas and Parana forests: D. hymenoides, D. krausii and D. reptans. The aim of this research was to characterise the morphoanatomy to better delimitate the taxa. Also, to evidence the presence of fungal endophytes. Conventional histological techniques were applied to fresh and FAA-fixed material. The anatomical structure of the different organs, in the three species, is similar; with collateral protostelic rhizomes, covered with simple or branched rhizoids; stipes teretes with glandular trichomes; uniestratified laminae formed by epidermal cells, with collateral vascular bundles; false veins formed by macrosclereids and stegmata or only by macrosclereids. The eglandular and glandular trichomes on the lamina differ in the species studied. The basal and middle portion of the involucre are pluristratified, with a vascular bundle at each margin, while the apical portion is formed by a one layer of epidermal cells; the receptacle is pluristratified with glandular trichomes on its surface. The presence of stegmata, collenchymatous tissue, sclerenchyma, mucilage fibers in phloem, pores in lamina and cuticle on the epidermis is evidenced and reported. Septate fungal endophytes were observed in epidermal cells of the rhizome, stipe and lamina of D. krausii and D. reptans. Species are differentiated by the following characters: shape of the lamina, diameter of the rhizome, number of false veins and the types of trichomes and pores. A key for the studied species is presented.