Pilularia
Pilularia, commonly known as Pillwort is an aquatic/semi aquatic genus of fern that belongs to the family Marsileaceae. It consists of five recognised species with one endemic to Australia, Pilularia novae-hollandiae.
The IUCN red list of threatened species defines Pilularia globulifera as near threatened and Pilularia minuta as endangered.
Of the Australian states in which Pilularia is present, it is locally classified as rare in Tasmania and South Australia, endangered in New South Whales and not threatened in Western Australia.
Rare and endangered species in South Australia, Tasmania and New South Whales are threatened by swamp drainage, infrastructure/roadside disturbance and competing species of grass.
Pilularia consists of several thin grass-like stalks that lack leaves shooting up from a creeping rhizome, forming small green bunches. Pilularia is a simple fern in comparison to its close taxonomic neighbours. Green rhizomes grow horizontally below the surface of the ground, forking in multiple directions and forming dense, branched clumps. The fronds grow upright from rhizomes with a mature length of 2 – 7 centimetres and are green to dark green in colour. They are simple and slender in nature with a single vein running up the centre. These fronds form single or grouped batches with the young fronds curling at the tips. Pilularia is a heterosporous fern, meaning it produces two types of spores (micro and megaspores) of different size and sex. A single sporocarp forms on the rhizome, often buried beneath the substrate. The sporocarp comprises of scaly tissue with a hard and woody texture. The capsule opens when filled with water, releasing megaspores (egg-shaped structures that develop into male gametophytes) which are fertilized by microspores (circular-shaped structures that develop into female gametophytes) released simultaneously. The sporocarp is partially protected by a thin, translucent layer know as the indusium. Spore dispersal is aided by wind and fauna such as sea birds (Jones, 1998).
Pilularia is a closely related genus to Marsilea and Regnellidium. Taxonomic and morphological similarities link the genera as monophyletic taxon, which represent a group of organisms descendant from a common ancestor (Nagalingum et. al, 2008). The evolutionary patterns between genera were evaluated using heterochrony, accelerated growth and early termination of simplified leaves (Pryer and Hearn, 2009). The later, more complex stages of ancestral species were lost, resulting in the simplified leaf structure of Pilularia. Marsileaceous ferns, including Pilularia exhibit accelerated maturation, high reproductive rates and the occupation of ephemeral (changing) habitats (Pryer and Hearn, 2009).
-Plantae
-Tracheophyta
-Polypodiopsida
-Salviniales
-Marsileaceae
-Pilularia
(Species 2000 and ITIS Catalogue of Life: April 2013)
Pilularia ranges from Northern temperate regions to the southern hemisphere in areas such as North and South America, New Zealand and Australia.
Figure 1: West Australian distribution of Pilularia (This image was retrieved from https://florabase.dpaw.wa.gov.au/browse/profile/20913)
It is an aquatic/semi-aquatic fern that resides in mud and silt of shallow pools/swamps and seasonal margins of rivers and creeks (Jones, 1998).
Pilularia currently has no known commercial uses.
However, there have been records of indigenous use as food by removing and grinding the sporocarps.
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