The Flowering Plants of Hawaii
Part 36 Plantaginaceae - Plumbaginaceae - Polemoniaceae
The Hawaiian Islands are home to five naturalized and three endemic species in the Plantaginaceae. The naturalized species are, for the most part, cosmopolitan, or at least widespread, weeds, and are well known to gardeners. Plantago pachyphylla (see image), the most common of the three endemic species, occurs in a variety of habitats including wet forests, bogs, and alpine grasslands. More restricted is P. princeps, which is thought to exist in four different forms (varieties). Plantago princeps var. laxifolia (see image), photographed on Maui, occurs in wet sites or steep cliffs on Kaua`i, O`ahu, Moloka`i, and Maui. In Hawaiian this plant is known as laukahi kuahiwi or ale. Laukahi is the Hawaiian name for broadleaf plantain; kuahiwi tells us that it is a laukahi from the highlands. Ale is a specific name for this plant. Plantago hawaiensis (see images), listed as endangered, is restricted to dry sites on the Big Island. Efforts are being made to replant this species in exclosures on Mauna Loa where the photograph was taken. In the absence of alien herbivores, this plant takes well to reestablishment. This species is also known as laukahi kuahiwi.
The origin of the Hawaiian members of the genus was described by R. K. Hoggard and coworkers (2003) based upon a study combining DNA sequence data and morphological features of representatives from the range of the genus. Their analysis showed that at least four of the North American species (of section Plantago) arose from an Asian ancestor. Subsequent to the diversification of the North American species, a long distance dispersal event gave rise to the progenitor of the Hawaiian species. The next stage in the development of the Pacific Basin species involved further long distance dispersal from a Hawaiian plant to the South Pacific Islands.
A recent study by Stephanie Dunbar-Co and coworkers (2008) at the University of Hawai`i using sequence data from four chloroplast genes provided very strong evidence that the Hawaiian endemic species have resulted from a single colonization, likely on Kaua`i, with subsequent inter-island movement to younger islands and diversification into the array of forms recognized today. These workers suggest that formal recognition of discrete morphologically identifiable units within P. pachyphylla would be supported by the data. Authors of the Manual noted the highly variable nature of this species and suggested that such recognition required additional information.
Although it is not relevant to the purposes of this book, it is worthwhile pointing out that Plantaginaceae have undergone a massive reorganization based upon extensive DNA sequence analyses. Authors of the Manual present the classical view of the family as consisting of about 250 species in three genera, whereas the DNA-based view of the family has some 1,900 species in 101 genera (Mabberley, p. 675-676). Readers interested in these radical changes should consult the comprehensive work by Douglas Soltis and colleagues (2005).
Plumbaginaceae, the plumbago or leadwort family, are represented in the Hawaiian Islands by a single species, Plumbago zeylandica, `ilie`e, hilie`e, or `ilihe`e (see images), which is native to Old World tropics and to the islands. This species grows in dry, often disturbed, sites and is occasionally planted as a decorative plant (unless the specimens I saw were weeds in a garden; they seemed attractive enough with their pale blue flowers).
The phlox family, Polemoniaceae, are represented in the islands by a single naturalized species, Gilia capitata, whose normal home range extends from British Columbia south to California. Apparently, it is known only from sites on East Maui (Haleakalä). I am familiar with this plant in its home range, but I have never seen it on Maui.