Palaeos		Lycopodiophyta
Plants		Pleuromeiales

Order Pleuromeiales

This extinct paraphyletic group, 1 to 2 meters tall, were reduced relatives of the Lepidodendrale lineage. They were heterosporous and bore ligulate leaves.

With the late Carboniferous (Kazimovian) drying out of the climate the mighty scale trees disappeared and smaller unbranched "woody" plants like Chaloneria and Pleuromeia continued to flourish throughout the Permian and into the Early Triassic.

Although large specialized lycopsid trees (Lepidodendrales) dominated the Carboniferous swamps, they were dependent on very wet environments, and inevitably died out as the climate changed during the Late Pennsylvanian and into the Permian.

Smaller, unbranched forms like Chaloneria cormosa of the Upper Pennsylvanian (Kazimovian Epoch) of western euramerica fared better. This species was up to 2 meters in height with axes up to 10 cm in diameter. It is structurally quite similar to representatives of the Pleuromeiaceae (Triassic period). Typha latifolia may be a synonym. It was unbranched with a terminal fertile zone for spore production, and grew in dense strands in swampy areas. The base of the plant was similar to the base of the corm in Isoetes (roots of the Stigmaria-Isoetes type). It is known from North American coals balls.

This family of extinct lycopsids is made up of several Mesozoic genera and would seem to be allied with the Isoetaceae. They were small trees of around a meter in height with a branchless trunk, possibly transitional between the Carboniferous Lepidodendrales and the Isoetales. The family Pleuromeiaceae is variously included among other order, as well as its own order. There is also distinct similarity between Pleuromeia to Chaloneria. However, the Pleuromeiales are not known from anatomically preserved species, so our knowledge of them is somewhat more limited than for Chaloneria. The lower part of the plant resembles Isoetes. Pleuromeia is structurally intermediate between the Paleozoic genus Sigillaria and the Cretaceous genus Nathorstiana.

Pleuromeia is known from fossil remains from Germany, Russia, Australia, Japan, and China and without doubt had a global distribution.  These plants, the last humble representatives of the great Lepidondendrales,  grew in monotypic stands in coastal swamps, before succumbing to the increasing aridity of the later Triassic age.

Nathorstiana - This Early Cretaceous plant is sometimes included in the Pleuromeiaceae but resembles Isoetes, especially in the leaves and the base of the stem. although a distinct stem region is still present. The roots were of the Stigmarian type. It was about 10 to 30 cm in height.

Links

VASCULAR PLANT MORPHOLOGY LABORATORY 4 Class Lycopsida

Bateman, R.M., W.A. DiMichele and D.A. Willard. 1992. Experimental cladistic analysis of anatomically preserved arborescent lycopsids from the Carboniferous of Euramerica: An essay on paleobotanical phylogenetics. Ann. Missouri Bot. Gard. 79: 500-559.

Wagner, W.H., Jr. and J.M. Bietel. 1992. Generic classification of modern North American Lycopidiaceae. Ann. Missouri Bot. Gard. 79:676-686.