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Information about Australia's flora - Ferns of Australia and PNG
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Psilotum Sw.

Terrestrial or epiphytic herbs of small to moderate size. Rhizome shortly creeping, much-branched, protostelic, lacking roots, densely covered with fine rhizoids. Stems triquetrous, rigid and erect, to flattened, flaccid and pendulous, photosynthetic, linear, simple towards the base, repeatedly dichotomous upwards, siphonostelic. Leaves (sterile lateral appendages) simple, minutes, scale-like, lacking a midrib, scattered along the stem in 2 or 3 rows. Synangia globular, 3-lobed, composed of 3 fused sporangia, borne in the axils of minute, scale-like appendages similar to the leaves, exindusiate, homosporous, each lobe dehiscing by a radial slit. Spores monolete, finely reticulate.

Species in Papuasia

1a. Stems triquetrous, short and erect or arching, c. 1 mm wide; plants terrestrial or epiphytic... P. nudum
Stems flattened, long and pendulous, c. 2 mm wide; plants epiphytic... P. complanatum