Taisha is the author of today’s entry. She writes:
Today, we have two photographs of the Hawai’ian Trematolobelia kaalae (photo 1 | photo 2). They were taken by David Eickhoff@Flickr last May, and uploaded to the Botany Photo of the Day Flickr Pool. Thanks David!
Trematolobelia kaalae is endemic to the Wai’anae Mountains of O’ahu. It is perhaps most easily found on the upper slopes and summit of Ka’ala (its namesake), growing in wet shrubland. Plants will grow to about 2 metres in height at maturity. Once mature, plants will blossom from mid-March to late May with pink flowers. Most other members of Campanulaceae (bellflower family) on Hawai’i are autumn-blooming.
Evidence to-date reveals that the Campanulaceae of Hawai’i form the largest plant clade, or the largest grouping of species originating from a single ancestor, of any single oceanic island or archipelago. With 126 species in 6 genera, these Hawaiian endemics (known collectively as the Hawaiian lobeliads) are an example of an impressive adaptive radiation in plants. A recent study suggests that this monophyletic group originated from a single colonization event about 13 million years ago. After colonization, radiation (or diversification into new taxa), began quickly. The first split occurred after only 0.3 million years, and all genera diverged by 9.76 mya based on top-down calibration (6.97 mya for bottom-up calibration). Trematobelia was among the last to diverge (i.e., it is among the most recently-evolved), along with Lobelia sect. Galeatella.
The diversity of the Hawai’ian lobeliads is outstanding across species, including high-elevation bog rosette-forming species, cliff-dwelling succulents, and forest & bog shrubs. Taxa vary widely in leaf and floral morphology as well. Floral diversity is seemingly associated with a species’ ability to disperse seed. The lowest overall diversity and percent single-island endemism is found in lineages that are wind-dispersed, including Trematolobelia, while the highest diversity and percent endemism occurs in genera with fleshy fruits that are poorly dispersed by birds, like Cyanea (see: Givnish, T.J., et al. 2009. Origin, adaptive radiation and diversification of the Hawaiian lobeliads (Asterales: Campanulaceae). (PDF) Proc. R. Soc. B 276:407- 416.
For a thorough overview of speciation and adaptive radiation, refer to Givnish’s article from 2010, Ecology of plant speciation (PDF), published in Taxon 59(5):1326-1366.