Figure 3.22. (top) Evolution of growth form in the genus Psychotria may involve one of two possible
scenarios regarding the character of branched habit. In pathway A, developmental suppression of
"adult" (woody, branched) habit in "neotenic" intermediate species and subsequent release of
suppression in epiphytic forms is suggested. An equally likely alternative, shown in pathway B,
involves retention of adult branched form in the epiphytic lineage and independent gain of the
neotenic unbranched form in two separate lineages of the rest of section Notopleum. Figure 3.23.
(bottom) Psychotria uliginosa Sw. is the type species for Psychotria section Notopleura and bears the
succulent unbranched growth form that characterizes this group. This species is common in the
Monteverde Cloud Forest Preserve and surrounding community.3 m, members of section Notopleura are usually less
than 1 m tall. Further stratification occurs by radiation
of epiphytic forms into the canopy (Figs. 3.23, 3.24).
Such stratification has implications for pollination
biology and maintaining reproductive isolation in sym-
patric taxa. Many congeneric species are sympatrically
distributed in the tropics, and spatial isolation as well
as temporal partitioning (Grant 1981) may play a role
in maintaining reproductive isolation and hence spe-
cies richness in this genus.
Epiphytism has evolved at least twice in separate
lineages in the genus Psychotria, once in the neo-77 Plants and Vegetation