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.

Didymoglossum（Hymenophylllaceae）是一个单系属，包括小型附生或附生植物。在永加斯和巴拉那森林的南部地区发现了三种形态非常相似的物种：D. hymenoides、D. krausii和D. reptans。这项研究的目的是表征形态解剖学特征，以更好地界定分类单元。此外，还可以证明内生真菌的存在。传统的组织学技术应用于新鲜的和 FAA 固定的材料。这三个物种的不同器官的解剖结构是相似的；有侧生的原骨根茎，覆盖有单根或分枝的根茎；柄圆柱状具腺毛；由表皮细胞形成的单层薄片，具有侧支维管束；由大巩膜和柱状体形成或仅由大巩膜形成的假静脉。叶片上的无腺毛和腺毛在所研究的物种中有所不同。总苞的基部和中部为复层，边缘各有维管束，顶端部由一层表皮细胞组成；花托是多层的，其表面有腺毛。已证实并报道了剑柱、厚角组织、厚壁组织、韧皮部中的粘液纤维、薄层中的孔以及表皮上的角质层的存在。在克劳氏石斛和雷普坦石斛的根茎、柄和叶片的表皮细胞中观察到有隔膜的内生真菌。物种通过以下特征来区分：叶片的形状、根茎的直径、假脉的数量以及毛和孔的类型。给出了所研究物种的关键。