JUNE 1966 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 11(2): 173-276 



Acromastigum Evans, Bull. Torrey Club 27: 103. 1900, emend. Evans, 

 Ann. Bryol. Suppl. 3: 5. 1934. 



Mastigobryum p p.p., G. L. & N. Syn. Hep. 218. 1845. 



Mastigobryum [sect.] III. Inacquilatera Stephani, Hedwigia 25: 245. 1886. 

 Bazzania sec. III. Inaequilaterae Schiffner in Engler & Prantl, Nat. Pflanzenfam. I 3 : 

 101. 1893. 



Mastigobryum [subg. Inacquilatera] Stephani, Bull. Herb. Boissier II. 8 : 404. 1908. 



Plants of small to medium size, prostrate to ascending, loosely branched in 

 apparent dichotomies; vegetative branches lateral, leafy, of the Frullania type, 

 with the dorsal ovate half-leaf subtending the stem and branch, or ventral 

 flagelliform, of the Acromastigum type, with the ovate half-underleaf adjacent 

 to the base of the branch on either side: sexual branches very short, ventral inter- 

 calary, in the axils of the underleaves (rarely on flagelliform branches) ; stem in 

 transverse section with one layer of large cortical cells with thicker walls 

 surrounding the medulla of many smaller cells; leafy branches with a unistratose 

 cortex of only seven large cells with thick walls, surrounding the medulla of many 

 smaller cells. Rhizoids colorless, with branched tips, from the bases of the 

 underleaves, the scales of the flagelliform branches, and the base of the female 

 inflorescence. Line of leaf insertion transverse to oblique, the leaves incubous. 

 Leaves rectangular to ovate in outline, undivided, bidentate or bifid, with the 

 segments unequal or rarely equal, in some species vittate, the cell-walls thickened. 

 Underleaves transversely inserted, undivided, bifid or trifid. Plants dioicous; male 

 branches short, catkin-like, often curved, the bracts smaller than the leaves, 

 usually bidentate, concave, of delicate texture, monandrous, the bracteoles similar, 

 smaller, less concave, without antheridia; female branches without innovations, 

 the bracts and bracteoles different from the leaves, in three or four series, ovate, 

 with two main divisions, variously laciniate, lobate, or dentate, the innermost 

 series the largest. Perianth unistratose (usually) , terete below, trigonous above, 

 the keels broad, with the third keel ventral, the mouth more or less plicate, 

 3-lobed, with marginal laciniae and cilia. Shoot/sporophyte relationship a shoot- 

 calyptra. Capsule oval, the wall of four layers of cells, the outermost layer with 

 brown knot-like thickenings most numerous on the longitudinal radial walls, the 

 innermost layer with crowded brown semi-annular thickenings as bands on the 

 inner tangential walls; elaters bispiral; spores brown, minutely verruculose. 

 Sporophyte stalk of eight longitudinal rows of large cells surrounding many rows 

 of smaller cells. 



Type species: Mastigobryum (?) integrifolium Austin. 



The species belong to the section Inaequilaterae, in which the cortical cells of 

 the leafy branches are in seven longitudinal rows, the leaves are bifid, and the 

 underleaves trifid. 



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