Abstract
Two species of Coprosma (Rubiaceae) J.R.Forst. & G.Forst. are described from the island of Maui of the Hawaiian Archipelago. A newly described taxon, Coprosma cordicarpa J.Cantley, Sporck-Koehler, & M.Chau, sp. nov. is locally common in medium to high elevation dry forests and shrublands of leeward East Maui. The second taxon is resurrected from the synonymy of Coprosma foliosa A.Gray as Coprosma stephanocarpa Hillebr. and occurs in mesic to wet rainforests of both East and West Maui. Both taxa are segregated from Coprosma foliosa, with which they share similar morphological characters. A conspicuous and persistent calyx of the fruit and various floral characters most easily differentiate both taxa from other Hawaiian taxa. The newly described Coprosma cordicarpa is further distinguished from Coprosma stephanocarpa by a central constriction of the fruit with a depressed apex, which gives it a characteristic heart shape. Furthermore, the taxa are largely separated phenologically, ecologically, and geographically. Descriptions, conservation status, and specimens examined for the new species are included.
Highlights
There are more than 110 species in the genus Coprosma J.R
Herbarium specimen measurements, and an in-depth literature review, it was concluded that the two C. foliosa segregates, C. cordicarpa and C. stephanocarpa, maintain rather consistent morphologies on leeward East Maui (C. cordicarpa) and mesic areas of East and West Maui (C. stephanocarpa)
They can be segregated from the variable C. foliosa s.l. found on other islands and effectively replace C. foliosa s.l. on East Maui, at least one form of C. foliosa s.l. is still found on West Maui
Summary
There are more than 110 species in the genus Coprosma J.R. Forst. & G.Forst., which consists of species that are predominantly dioecious and wind pollinated. The orangefruited Hawaiian Coprosma taxa—known locally as pilo in the Hawaiian language— were determined to be most closely related to the six Marquesan species and one (of two) species from Rapa Iti of the Austral Islands. Together, these taxa (from the Hawaiian Islands, Marquesas Islands, and Rapa Iti) were found to be more closely related to taxa in New Zealand than to other species on islands elsewhere in the Pacific where Coprosma taxa occur (i.e. Austral Is., Cook Is., Fiji, Kermadec Is., Lord Howe I., Norfolk I., Pitcairn I., Samoa, Society Is., and Vanuatu). No resolution among Hawaiian taxa was recovered by Cantley et al (2014), which they suggest is because the colonization event to the Hawaiian Islands by the orange-fruited Coprosma ancestor occurred after the emergence of Kaua‘i (≈5 Ma). Few detectable genetic mutations have since accumulated, which made it difficult to resolve recently diverged evolutionary relationships from the methodology that was used
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