Kingdom Plantae Class Pteridopsida Family Pteridaceae Scientific name Platyzoma microphyllum | Division Pteridophyta Order Polypodiales Subfamily Pteridoideae Rank Genus | |
Similar Loxsomataceae, Cystodium sorbifolium, Osmundales, Matoniaceae, Culcitaceae | ||
Platyzoma microphyllum, the sole species in genus Platyzoma, is a fern native to northern Australia. It occurs in the Kimberley region of Western Australia; in the Northern Territory and Queensland, and in northern New South Wales, where it is considered endangered. Vernacular names include Braid Fern.
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Characteristics
Platyzoma is unusual among ferns in that it may display incipient heterospory.
Microsporangia produce 32 microspores, each 71-101μm in diameter. Megasporangia produce 16 megaspores, each 163-183μm in diameter. Microspores produce a filamentous microgametophyte, which lacks rhizoids and gives rise only to antheridia. Megaspores produce spatulate megagametophytes with rhizoids, which produce archegonia. Megagametophytes may later produce antheridia, making them functionally bisexual. Development of gametophytes is not endosporic.
Taxonomy
Platyzoma is usually placed in the family Pteridaceae, but some botanists place it alone in Platyzomataceae. Tryon has speculated that Platyzoma, with its incipient heterospory, unusual chromosome number (2n=78) and other features may represent a stage transitional to the heterosporous aquatic ferns.
In 1827 Nicaise Auguste Desvaux included in Platyzoma additional species, such as Gleichenia alpina, Gleichenia dicarpa and Gleichenia rupestris, which are currently regarded by most scholars as part of the genre Gleichenia.
A more recent treatment by Christenhusz et al., 2011, placed Platyzoma within the Pteridaceae genus Pteris and transferred the Platyzoma microphyllum R.Br. 1810 to Pteris platyzomopsis Christenh. & H.Schneid. 2011