Question

Synangia of Psilotum

Answer 1

The division Psilotophyta contains two living genera including Psilotum and Tmesisteris. Although there is some uncertainty in the evolutionary relationship of Psilotophyta, they are thought to be close allies with ferns. The Psilotum sporophyte is simple morphologically. Some simple characteristics found in Psilotum that are similar to their ancestors in the Rhyniophyta and Trimerophyta divisions include a dichotomously branching sporophyte, no leaves, no roots, an exarch protostele, and terminal sporangia. Psilotum nudum, commonly known as the whisk fern, is found in the tropics and subtropics. Psilotum is eusporangiate and meiosis results in homosporous spores. The spores are produced in sporangia that are usually aggregated in groups of three, but sometime range from two to six. The fused sporangia are called synangia and are borne on short stems, subtended by short scale-like outgrowths called enations.