Bryophytes on Lava Flows — Miller 
247 
characteristic of mountain tops. Comparative 
physiological studies of several populations 
would be most interesting in this regard. 
The species of Campylopus , Rhacopilum, 
Rhacomitrium , and Grimmia previously men- 
tioned are true pioneers which establish them- 
selves on bare lava rock. However, other mosses 
appear on relatively new lava flows in pockets 
where dust collects to form a minute patch of 
soil. The plants which colonize this type of 
microhabitat are mosses of world-wide distribu- 
tion which might aptly be called "weeds.” 
Funaria hygrometrica is the only such species 
found in Doty’s collections, although Bryum 
argenteum and Ceratodon purpureus have been 
found on essentially barren lava flows in sim- 
ilar circumstances. 
The classical concept of lichen-moss-herb- 
shrub-tree succession does not apply in Hawaii 
on new lava flows. Mosses are true rock pioneers 
and lichens are rather limited in their establish- 
ment. In general, a few species of bryophytes 
become established in suitable microhabitats 
and never form an extremely conspicuous part 
of the vegetation. In fact, it would seem to one 
who has observed Hawaiian lava flows that 
plants are established wherever and whenever 
suitable habitats exist for the disseminules which 
reach these habitats. Thus, no exact plant suc- 
cession of one plant replacing another can be 
established. With the establishment of vascular 
plants, new microhabitats become available and 
such moss species as Macromitrium brevisetum, 
M. emersulum, Fissidens spp., Bryum spp., Pohlia 
spp., Ectropothecium sandwich ense, and Ves- 
icularia graminicolor become established on rock 
in mesophytic regions. Often the leafy liverwort 
Brachiolejeunea sandvicensis becomes estab- 
lished at the same time as the mosses listed 
above. Another liverwort, Riccia rechingeri, was 
recently discovered in soil pockets in the Kau 
desert and may be discovered in similar hab- 
itats on newer flows. As soil is necessary for 
the growth of this plant, it probably should not 
be considered a true pioneer species. 
