Plagiogyriaceae

Description

Terrestrial ferns, small to medium sized, 10-150 cm, rarely up to 2 m high, devoid of scales.

Distribution

Plagiogyria has an interesting amphi-Pacific disjunct distribution. In Asia it occurs north from Japan, South Korea (Cheju Island), to South China, westwards to East Himalayas ending on the south slope of Central Himalayas, in India only common at the far eastern corner, not extending southwards on the subcontinent, and eastwards extending southwards via Indochina to Malesia, the Bismarck Archipelago, and the Solomon Islands. In tropical America it is found from Mexico to the Caribbean and the Andes of Venezuela, extending south to Bolivia and southeastern Brazil. The present distribution centre of Plagiogyria is in South and Southwest China. Eight species are found in China, most very common and abundant. Plagiogyria assurgens is the only species endemic to China. Second to China, six species and one variety are found throughout the Philippines and, except the one variety shared with Borneo, all six species are shared with Taiwan and South to Southwest China. This distribution is not often found in other groups of ferns. Those six species reached the Philippines perhaps by way of mainland China via Taiwan. Iwatsuki & Price (1977) commented that the Himalaya-Taiwanese floral component of northern Luzon is not a relict but recent. It is noted that P. falcata, P. euphlebia, and P. stenoptera in the Philippines are restricted in distribution and their populations are small. Japanese islands are also very rich in species; five occur there and all are rather common, except P. stenoptera which is found only in Yakushima Island. This species has a disjunct distribution between SW China, Taiwan and northern Luzon, and this case falls within many other examples of ferns that have a disjunctive distribution from SW China or East Himalayas to Taiwan and Japan. Plagiogyria matsumureana, an interesting endemic Japanese species, is the only summer-green species of Plagiogyria. It is the only extant relative of the tropical American species, P. pectinata. These two species are so similar that they are nearly unseparable morphologically and it seems that the only possible explanation of the origin of the American species is that it is derived from a common ancestor in Asia. Unlike the Sino-Himalaya, or Sino-Japan distribution groups, Plagiogyria is not well developed in the Indian subcontinent. The fact that none of them occurs in Africa, Australia and the lower part of India may shed light on the explanation of the historical biogeography of Plagiogyria. A few species in the north and northeastern corner of India are probably recently dispersed from the east. Plagiogyria has a wide extension in the islands of SE Asia, but most species are restricted to higher mountain forests. The four distinct local varieties of P. egenolfioides are morphologically and ecologically different. Plagiogyria egenolfioides var. sumatrana is distributed from Sumatra to Peninsular Malaysia, not uncommon at 1300-1800 m high ridges. The plants are usually large, the leaves have an elongate pinna-like apex and resemble P. euphlebia. Plagiogyria egenolfioides var. decrescens is the commonest high altitude fern in New Guinea and ranges from 1800 to about 4000 m. In the summit grasslands, this variety forms large dense populations often associated with Blechnum vestitum and it reaches eastwards into the Solomon Islands, and to the north into the Moluccas (Seram). Two other varieties occur in Borneo, the Philippines, Sulawesi, and east to Seram. In the Pacific P. egenolfioides var. decrescens and P. glauca were once collected on the summit of Mt Popomanatsen in Guadalcanal (Solomon Islands). The geographic distribution may be explained by the fact that all Plagiogyria species are mountain plants, abundant on cold, moist, forested high ridges. Most, if not all, are growing in acid peaty soil (Holltum 1966). Most of the plants can form large dense populations, and are dominant herbs in the undergrowth. Some species have a forked rhizome, or form runners to propagate vegetatively.

Taxonomy

Plagiogyriaceae is a monotypic family in the leptosporangiate Pteridophyta.

Synonymy

Plagiogyriaceae Bower in Ann. Bot. 40: 484. 1926