Pittosporum halophilum Rock (Pittosporaceae: Apiales): Rediscovery,Taxonomic Assessment, and Conservation Status of a Critically Endangered Endemic Species from Moloka‘i, Hawaiian Islands

Abstract

Pittosporum halophilum Rock originally was known only from the type collections made in 1910 and 1911 along the windward sea cliffs of Moloka‘i. In the most recent revision of Hawaiian Pittosporum it was treated as synonymous with the more common species P. confertiflorum A. Gray. Since 1994, several plants fitting the circumscription of P. halophilum have been discovered near the type locality. Careful studies of these individuals and of plants cultivated from their seeds clearly revealed that they are not only characterized by salt tolerance, but differ from P. confertiflorum also in several other characters (i.e., a small, shrubby habit; smaller leaves with cuneate bases and unique tan to golden yellow wooly dense tomentum on abaxial leaf surfaces; shorter petioles; subcuboid to ovoid capsules; and, in most individuals, functionally unisexual flowers). Based on these substantial differences we conclude that P. halophilum merits recognition on species level. In this paper we give a detailed description of P. halophilum including remarks on its conservation status.