They are magnificent evergreen trees, with apparently whorled branches, and stiff, flattened, pointed leaves, found in Brazil and Chile, Polynesia and Australia.
The Ulvaceae, the thallus of which consists of external form as an expanded Coprinus, Neomeris simulates the laminae, one or more cells thick, or hollow tubes, probably represent fertile shoot of Equisetum with its densely packed whorled branches, a still more advanced stage in the passage of a colony into a multiand in Microdictyon, Anadyomene, Struvea and Boodlea the branches, cellular plant.
Attached to the bottom of pools series of the Confervales, the thallus consists of filaments branched by means of rhizoids, the thallus of Characeae grows upwards by or unbranched, attached at one extremity, and growing almost means of an apical cell, giving off whorled appendages at regular wholly at the free end.
To take an example, Lemanea and Batrachospermum are Florideae which bear densely-whorled branches, but which, on the germination of the carpospore, give rise to a laxly-filamentous, somewhat irregularly-branched plant, from which the ordinary sexual plants arise at a later stage.
The leaves are generally simple, often with a toothed margin; their arrangement is alternate, opposite or whorled, all three forms occurring in one and the same genus Lysimachia.
Such whorled or verticillate bracts generally remain separate (polyphyllous), but may be united by cohesion (gamophyllous), as in many species of Bupleurum and in Lavatera.
The non-cellular order Siphoneae is fairly well represented in Palaeozoic strata, especially by calcareous verticillate forms referable to the family Dasycladeae; the separate tubular joints of the articulated thallus, bearing the prints of the whorled branches, are sometimes cylindrical (Arthroporella, Vermiporella, &c.), sometimes oval (Sycidium) or spherical (Cyclocrinus).
The long, slender stems, somewhat tumid at the nodes, were ribbed, the ribs running continuously through the nodes, a fact correlated with the superposition of the whorled leaves, the number of which in each verticil was some multiple of 3, and usually 6.
The smaller branches bear the whorled leaves, probably four in each verticil.
The fructification consists of long, lax spikes, with whorled sporophylls; indications of megaspores have been detected in the sporangia.
An Equisetaceous plant, which Brongniart named Phyllotheca in 1828, is another member of the same flora; this type bears a close resemblance to Equisetum in the long internodes and the whorled leaves encircling the nodes, but differs in the looser leaf-sheaths and in the long spreading filiform leaf-segments, as also in the structure of the cones.