See ad 
; are 
210 Evans: HEPATICAE OF PUERTO RICO 
involucre, also, a single bracteole is present for the pair of bracts 
(PLATE 16, FIGURE I), just as in other genera of the Lejeuneae. 
It is evident, therefore, that the spiral arrangement of the leaves 
is the primitive one and that the zigzag arrangement represents a 
later development. 
In spite of its duplicated underleaves Diplasiolejeunea has 
many characters in common with Cololejeunea and Leptocolea, in 
which. no underleaves whatever are developed. In fact, the 
authors of the Synopsis Hepaticarum included in their subsection 
Duplicatae, which is one of the groups into which they divided 
their § Typicae of the genus Lejewnea, two species of Leptocolea 
as well as several species of Diplasiolejeunea. Gottsche afterwards 
grouped together all the Lejeuneae known to him in which the 
uriderleaves were duplicated, some of which naturally belong to 
the genus Colura.* Spruce, however, was the first to define 
Diplasiolejeunea in its present sense. He included it among the 
subgenera of Lejeunea,} but it was soon raised to generic rank by 
Schiffner. t 
The genus is widely distributed in tropical regions and contains 
about twelve species. The type species, D. pellucida (Meissn.) 
Schiffn., is abundant in America and is known also from Africa, 
the East Indies, and New Caledonia. Three of the other species 
are African, one is known from Tasmania only, and the others are 
American. Although the plants attain a fairly large size for 
members of the Lejeuneae they are delicate in texture and show 
little or no pigmentation. They grow on bark and on living leave 
and at least some of the species seem to be constant in their choice 
of a substratum. : 
The stems cling closely to the substratum and branch irregu- 
larly according to the usual Lejeunea or Radula type. The stems 
are at first scattered, but with the appearance of branches compact 
mats are gradually formed, the branches lying subparallel or divers” 
ing in a more or less radiate manner. The leaves are large 
usually loosely imbricated (PLATE 16, FIGURES I, 10, and 11). The 
lobes are attached by an exceedingly short and almost transvers€ 
Pie 
* Ann. Sci. Nat. Bot. V. 1: 164. 1864. 
T Hep. Amaz. et And. 301. 1884. 
¢ Engler & Prantl, Nat. Pflanzenfam. 13: 121. 1895. 
