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Significant differences between Psilotum and the rhyniophytes and trimerophytes are that the development of its vascular strand is exarch, while it is centrarch in rhyniophytes and trimerophytes. [13] The sporangia of Psilotum are trilocular synangia resulting from the fusion of three adjacent sporangia, [13] and these are borne laterally on ...
The sporangia of Psilotaceae are fused together into small and distinctive yellow balls called synangia (shown in the picture of P. nudum above). These synangia are located off the stems of the plants. They contain two sporangia each in Tmesipteris species, and three sporangia each in Psilotum species.
Synangia are 3 to 5 mm long. [3] The specific epithet truncata refers to the leaf tops, which appear abruptly cut off. [4] This plant first appeared in scientific literature in 1810 as Psilotum truncatum in the Prodromus Florae Novae Hollandiae, authored by the prolific Scottish botanist, Robert Brown.
A cluster of sporangia that have become fused in development is called a synangium (pl. synangia). This structure is most prominent in Psilotum and Marattiaceae such as Christensenia , Danaea and Marattia .
Psilotum nudum, the whisk fern, [3] is a fernlike plant. Like the other species in the order Psilotales, it lacks roots. [4]Its name, Psilotum nudum, means "bare naked" in Latin, because it lacks (or seems to lack) most of the organs of typical vascular plants, as a result of evolutionary reduction.
Tmesipteris, the hanging fork ferns, is a genus of ferns, one of two genera in the family Psilotaceae, order Psilotales (the other being Psilotum). Tmesipteris is restricted to certain lands in the Southern Pacific, notably Australia, New Zealand and New Caledonia.
Psilotum has been interpreted as producing sporangia (fused in a synangium) on the terminus of a stem. Equisetum always produce strobili, but the structures bearing sporangia (sporangiophores) have been interpreted as modified stems. The sporangia, despite being recurved are interpreted as terminal.
Leafless, dichotomously branching fossils bearing spines and possessing vascular tissue from the Devonian of Gaspé Peninsula, Canada, were thought by Dawson in 1859 to resemble the modern whiskfern, Psilotum. Accordingly, he named his new genus Psilophyton, the type species being P. princeps.