LOWER LAND PLANTS 



163 



Occurrence: about 14,000 species of world-wide 

 distribution; habitats range from completely aquatic 

 and submerged to very arid; typically are inhabitants 

 of drier areas, especially as an unstable plant com- 

 munity upon rocks and as a group of plants upon 

 tree trunks. 



PROTONEMA 



Resemble Chlorophyta in their organization; each 

 forms one to many buds, each bud germinating into a 

 gametophore. 



GAMETOPHORE 



Structure: normally attached to substrate; main 

 branches either erect or prostrate and erect; prostrate 

 branches form erect shoots which remain when pros- 

 trate branches die; branches with leaves; many 

 species with leaves forming gemmae and/or with pro- 

 tonema or root-like hairs forming usually dormant 

 gemmae (gemmae developing into gametophore only 

 after detached); sex organs occur among branch tips 

 or on short stalks from main stem; sex organs either 

 in a single cluster, or in separate clusters on the same 

 branch, on separate branches, or on separate plants. 



Leaves: variable; assuming most of the shapes of 

 the true leaves of higher plants (see Figure 11 .4) ; mid- 

 ribs when present are narrow and single, double, 

 forked, or very broad; midribs vary from not reaching 

 the apex to extending beyond as a hair-like structure; 

 leaves spirally arranged on branches, some leaves 

 appearing to lie in two rows (as in leafy liverworts) 

 but are spirally inserted upon the branches. 



Reproduction: reproductive organs develop from 

 the upper leaf cells; a male organ develops along with 

 one or more other cells that become larger, thicker- 

 walled, and more transparent to form a lid (oper- 

 culum); male organ usually requires moisture accu- 

 mulation for pressure to open the operculum and re- 

 lease sperm; female organ enlarges with sporophyte 

 growth, becoming a calyptra which is sporophyte- 

 enveloping, but the sporophyte growth finally tears 

 off the upper calyptra (calyptra usually covers sporo- 

 phyte capsule until capsule is nearly mature); the 

 torn calyptra may continue to develop and form a 

 prominent cap; asexual reproduction by leaf gemmae, 

 protonema and "root" gemmae, and by upright 

 branches growing when the prostrate branches die; 

 sexual reproduction follows same general pattern found 

 in all bryophytes. 



SPOROPHYTE 



Structure: a capsule, commonly supported by a 

 slender, short to long stalk, and a foot; sporophyte 

 does not persist long in the Sphagnales; capsule 

 normally covered for some time by a hood-like calyp- 

 tra; the capsule typically is an urn (main body) with 

 an apical opening that is often surrounded by a fringe 

 of fine "teeth" which project inward when wet and 

 outward when dry and the spores discharge; most 

 urns are capped by a circular lid (operculum), but 

 the urn and operculum are separated by a layer of 

 cells; drying and shriveling (perhaps moisture pres- 

 sure also) of the layer of cells and the lower oper- 

 culum sheds the operculum — but some species lack 

 an operculum; the calyptra and/or operculum may 

 be present or absent when the spores are shed; spores 

 are shed when the mature capsule (1) opens by split- 

 ting lengthwise, crosswise, or irregularly (Bryales); 

 (2) opens explosively often shooting operculum and 

 spores into the air (Sphagnales); or (3) opens mostly 

 along four regular lines (Andreales). 



There are more than twice as many mosses as all 

 other bryophytes. Mosses are widely distributed 

 upon moist surfaces from pole to pole. They range 

 from inconspicuous, thread-like masses (protonema) 

 to erect, fern-like plants almost 2 feet tall. Some large 

 specimens hang from trees or rocks, but the largest 

 (about 7 feet long) are the aquatic peat mosses. 

 Although the larger forms are potentially confusing 

 (they resemble spike or club mosses and ferns), 

 mosses have only root-like hairs, never roots. The 

 vast majority of species occur as tufts or extensive 

 cushions or mats on rocks, soil, or trees. 



Being bryophytes, mosses are dependent upon 

 moisture for sexual reproduction. However, they 

 persist in frigid and desert habitats. They have re- 

 markable abilities to survive freezing and desiccation. 

 Along with liverworts, they comprise an ecologically 

 influential part of localized Arctic floras. Although 

 they are like other bryophytes in not being marine, 

 some mosses persist in brackish waters. Therefore, 

 only flowering plants display a greater range of en- 

 vironments. However, mosses regularly grow in 

 habitats too severe for flowering plants. 



Temperate areas often have abundant mosses and 

 liverworts. In the Pacific Northwest and other areas 

 of high rainfall, they become so dense on rocks, soil, 

 and trees as to be called "moss forests." Above tim- 



