Introduction to the Andreaeopsida

the lantern mosses

Andreaea The lantern mosses (Andreaeopsida) are a basal group of mosses commonly found growing on exposed rock surfaces. They are able to cling to the rocks by their multicellular rhizoids, which delve into tiny cracks on the rock surface and anchor the plant. As in most mosses, the leaves of the latern mosses usually have a costa, or multilayered central supporting strand, though some species do not. The rest of the leaf is a single layer of cells, so that every cell is in close contact with the environment.

Mature latern mosses grow as clumps of small reddish to blackish brown plants. The dark pigments are located in the cell walls, and may help to reduce light damage caused by exposure in their rocky habitats -- most mosses require lower light levels for successful photosynthesis than other plants. The mosses are able to survive desiccation for long periods, and may recover even after being completely dried out. Such dessication would kill most other kinds of plants.

There are about 100 species of lantern moss, classified in two genera. The genus Andreaea includes all but one of these species, Andreaeobryum macrosporum (of Alaska and northwestern Canada). An additional genus Neuroloma (of Tierra del Fuego and South Georgia) has been renamed as a species of Andreaea. Most species grow in cool temperate to polar regions, and the majority are found in the Southern Hemisphere. They commonly are found growing in high, sunny alpine regions even in the tropics, though some other species prefer damp habitats. The preference of lantern mosses for rocky and alpine habiatats may explain why this apparently ancient group has left no fossil record.

Andreaeopsida have two distinctive features that separate them from other groups of mosses. First, the protonemata have a different structure. Protonemata are the earliest stage in growth of a moss from the spore, and in most mosses they grow as a network of filaments. In the Andreaeopsida, however, the protonemata are thallose, forming a multicellular flattened layer of embryonic cells.

In addition to protonemata differences, lantern mosses also release their spores differently. Most mosses produce a stalked capsule whose top falls off to release the spores, and a ring of flexible teeth around the opening to regulate spore release. The capsules of lantern mosses have no stalk, no cap, and no teeth. Instead, the capsule is elevated on an extension of the plant to which it is attached. This gametophytic extension is called a pseudopodium, or "false foot", and it pushes the capsule upwards so that spores may be dispersed further. The capsule itself opens by splitting lengthwise in four slits (sometimes 8), as you can see in the illustration above. The four partitions of the capsule wall between the slits bow outwards, expanding the slits and releasing the spores. A short columella ("little column") in the center of the capsule keeps the capsule wall from collapsing too far.

Composite illustration of Andreaea Hartmanii after Trotter.