5. Adaptive Radiation
69
2 Adaptive Radiation in Hawaiian Lobeliads
The Hawaiian lobeliads (Lobeliaceae) have long been viewed as one of the most
spectacular cases of adaptive radiation in plants on oceanic islands (Rock 1919;
Carlquist 1965, 1974; Lammers 1990; Givnish et al. 1994, 1995; Givnish 1998).
They include alpine rosette shrubs, succulent cliff plants, rain-forest and bog shrubs,
trees, and tree lets, and even a few epiphytes and vine-like species. They are the
angiosperm family with the largest number of taxa endemic to the Hawaiian Islands, with over 110 species in 6 genera, comprising one-ninth of the native flora
(Wagner et al. 1990; Lammers et a1. 1994). Most species were pollinated by honeycreepers, and many were dispersed by these or other groups of native birds (Rock
1919; Lammers and Freeman 1986; Givnish et a1. 1995).
The three endemic genera with fleshy fruits (Cyanea, Clermontia, Delissea)
encompass some 95 species and - based on gross morphology - are often considered the largest group of Hawaiian plants derived from a single immigrant, although the source of this immigrant is debatable (Rock 1919; Mabberley 1974,
1975; Lammers 1990). Cyanea (65 spp) is the largest angiosperm genus endemic
to Hawaii, and is comprised mainly of unbranched trees and treelets (1-18 m tall)
of mesic- and wet-forest interiors. Its tubular corollas are whitish to purplish and
15-80 mm in length, with a curvature strongly resembling the bills of the nectarfeeding honeycreepers that pollinated them. Its fruits are orange or purple in color,
and generally are less than 15 mm in diameter. Leaves vary from a few mm to 0.25
m in width; nearly one··third of the species have toothed, lobed, or highly dissected
margins, especially in the juvenile stage, accompanied by prickles along the leaf
veins and shoot axes.
Clermontia (22 spp) differs from Cyanea in having a branched, often shrubby
habit, and occurs mainly in forest edges and gaps rather than shaded understories.
Its orange fruits arc often more than 25 mm in diameter; its leaves are undivided
and unarmed; a few species (e.g., C. peleana) arc mainly epiphytic. Delissea (9
spp) bcars a narrow crown atop a tall stem, and occurs mainly in partially open dry
and mesic forests. Its flowers and fruits are similar to those of Cyanea; its petals
have one or more knob-like projections.
Among the capsular taxa, Lobelia sect. Galeatella includes four species of rosette shrubs of alpine bogs and wet openings; all have massive woody stems and
spectacular tcrminal inflorescences of large, tubular flowers, white or crimson in
color. Lobelia sect. Revolutella includes nine species of smaller shrubs of rock
walls, cliffs, ridges, and open forests; they bear smaller flowers with recurved petals that are tubular, and magenta to blue in color. Trematolobelia (4 spp) bears a
mop of linear leaves atop a short stem, and frequents wet ridges and openings in
wet or boggy forests. It has branched horizontal inflorescences and capsules with a
bizarre mechanism of dehiscence, opening by a network of ragged pores in the
capsule wall. Finally, Brighamia (2 spp) includes some of the most bizarre plants in
the world. Two rare species grow on sea cliffs on Kaua'i and Moloka'i, and bear a
cabbage-head of fleshy leaves atop an unbranched, succulent woody stem. Unlike
69
2 Adaptive Radiation in Hawaiian Lobeliads
The Hawaiian lobeliads (Lobeliaceae) have long been viewed as one of the most
spectacular cases of adaptive radiation in plants on oceanic islands (Rock 1919;
Carlquist 1965, 1974; Lammers 1990; Givnish et al. 1994, 1995; Givnish 1998).
They include alpine rosette shrubs, succulent cliff plants, rain-forest and bog shrubs,
trees, and tree lets, and even a few epiphytes and vine-like species. They are the
angiosperm family with the largest number of taxa endemic to the Hawaiian Islands, with over 110 species in 6 genera, comprising one-ninth of the native flora
(Wagner et al. 1990; Lammers et a1. 1994). Most species were pollinated by honeycreepers, and many were dispersed by these or other groups of native birds (Rock
1919; Lammers and Freeman 1986; Givnish et a1. 1995).
The three endemic genera with fleshy fruits (Cyanea, Clermontia, Delissea)
encompass some 95 species and - based on gross morphology - are often considered the largest group of Hawaiian plants derived from a single immigrant, although the source of this immigrant is debatable (Rock 1919; Mabberley 1974,
1975; Lammers 1990). Cyanea (65 spp) is the largest angiosperm genus endemic
to Hawaii, and is comprised mainly of unbranched trees and treelets (1-18 m tall)
of mesic- and wet-forest interiors. Its tubular corollas are whitish to purplish and
15-80 mm in length, with a curvature strongly resembling the bills of the nectarfeeding honeycreepers that pollinated them. Its fruits are orange or purple in color,
and generally are less than 15 mm in diameter. Leaves vary from a few mm to 0.25
m in width; nearly one··third of the species have toothed, lobed, or highly dissected
margins, especially in the juvenile stage, accompanied by prickles along the leaf
veins and shoot axes.
Clermontia (22 spp) differs from Cyanea in having a branched, often shrubby
habit, and occurs mainly in forest edges and gaps rather than shaded understories.
Its orange fruits arc often more than 25 mm in diameter; its leaves are undivided
and unarmed; a few species (e.g., C. peleana) arc mainly epiphytic. Delissea (9
spp) bcars a narrow crown atop a tall stem, and occurs mainly in partially open dry
and mesic forests. Its flowers and fruits are similar to those of Cyanea; its petals
have one or more knob-like projections.
Among the capsular taxa, Lobelia sect. Galeatella includes four species of rosette shrubs of alpine bogs and wet openings; all have massive woody stems and
spectacular tcrminal inflorescences of large, tubular flowers, white or crimson in
color. Lobelia sect. Revolutella includes nine species of smaller shrubs of rock
walls, cliffs, ridges, and open forests; they bear smaller flowers with recurved petals that are tubular, and magenta to blue in color. Trematolobelia (4 spp) bears a
mop of linear leaves atop a short stem, and frequents wet ridges and openings in
wet or boggy forests. It has branched horizontal inflorescences and capsules with a
bizarre mechanism of dehiscence, opening by a network of ragged pores in the
capsule wall. Finally, Brighamia (2 spp) includes some of the most bizarre plants in
the world. Two rare species grow on sea cliffs on Kaua'i and Moloka'i, and bear a
cabbage-head of fleshy leaves atop an unbranched, succulent woody stem. Unlike