(14 



MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



[VOL. 11 



leaves nearly equal to the leaves or smaller, approximate or imbricate, occasion- 

 ally reflexed, symmetric, bifid, the margins as in the leaves . Plants dioieous. 

 Male inflorescence terminal becoming intercalary on the stem or branch, the 

 bracts similar to the leaves, the lamina concave, the bracteoles similar to the 

 underleaves ; antheridia large, globose, mostly in pairs in the axils of the bracts, 

 the stalk six to eight cells long. Female inflorescence terminal on the stem or 

 branch, the bracts and bracteoles in three series, symmetric or nearly so, similar 

 to the leaves, larger, often more deeply divided and more strongly toothed, the 

 inner series sometimes smaller, often adnate and carried up on the perigynium ; 

 archegonia 8-10; sporophyte enclosed in a slender, hollow, cylindric, thick- 

 walled perigynium with a very short, reduced perianth at the top. Shoot/sporo- 

 phyte relationship a free, fleshy shoot-calyptra with old archegonia over its 

 surface. Sporophyte capsule ovoid-cylindric, the four valves spirally twisted, 

 the wall of three layers, the outermost layer of large cells with radially thickened 

 walls, the two inner layers of smaller cells with both radial and tangential 

 thickenings; seta long, thick; elaters long, tapering at the ends, bispiral, brown; 

 spores small, brown, smooth. 



Type species: Isotachis lyallii Mitten in J. D. Hooker, Bot. Antarct. Voy. 

 2(2): 149. 1855. 



A high degree of variability in size and color of the plants and in the size 

 and configuration of the leaves and underleaves and the teeth of their margins 

 is present in plants of many of the species. The latter was well illustrated by 

 Hatcher (1960), who made a comparative study of large numbers of the leaves 

 and underleaves of certain of the species. 



Some of the species formerly included in the genus have the general ap- 

 pearance and stem structure of an Isotachis but they produce perianths. The 

 genus Triandrophyllum was one of these groups of species. A few others have 

 not yet been transferred since the problem of relationships has not satisfactorily 

 been solved because the material is sterile. These latter, together with those 

 species for which no type has been available, are listed after the descriptions of 

 the species. 



Key to the Species 



1. Leaves without teeth or with a few scattered teeth. 



2. Leaves and underleaves more or less the same length, or the underleaves only 

 slightly smaller. 



3. Leaves different from the underleaves in outline; underleaves oblong, entire 



to emarginate; leaf sinus very broad, the lobes widely divergent. 12. I. splmdens. 

 3. Leaves and underleaves of similar form. 



4. Leaves and underleaves orbicular, cucullate, the very short segments incurved ; 

 plants small, dark brown, compact, more or less radially symmetric. 



16. I. spegaiziniana. 

 4. Leaves and underleaves ovate to ovate-truncate, sometimes broadly so. 

 5. Underleaf margin entire. 



6. Segments of the leaves and underleaves divergent; plants small, red to 



reddish-green; leaves bifid to one-half of their length. 1. I. tcnax. 



6. Segments of the leaves and underleaves not conspicuously divergent ; leaves 

 bifid to one-sixth of their length or less. 

 7. Sinus of the underleaf narrow, U-shaped, the segments acute, connivent ; 



leaves imbricate, patent; plants dark reddish-brown. 15. /. obtusa. 



7. Sinus of the underleaf broader, V-shaped, the segments rounded; leaves 



canaliculate, widely spreading; plants dark purple-brown. 14. I. lacustris. 

 5. Some underleaves with one or a few scattered marginal teeth. 



