Tetraplasandra lydgatei (Araliaceae): Taxonomic Recognition of a Rare, Endemic Species from O‘ahu, Hawaiian Islands

Tetraplasandra is a genus of seven species endemic to the Hawaiian Archipelago. Recent field studies in the Ko‘olau Mountains on the island of O‘ahu have led to a taxonomic reevaluation of a rare species, Tetraplasandra lydgatei. The species, originally described in the late 1800s, was placed into the widespread, polymorphic species T. oahuensis in a subsequent treatment of the genus. Several morphological characters and varying ecological habitats distinguish the two species. Based on these differences T. lydgatei deserves formal taxonomic recognition. Furthermore, T. lydgatei was an uncommon species even when it was originally described. This may be due to the early human alteration of the dry and mesic Hawaiian forests for housing and agriculture and also that the species was always only an occasional component of the mesic ecosystem. Regardless of the reasons, the rarity of this species has been accelerated. Currently, only six individuals of T. lydgatei are known to exist, and conservation efforts to protect it are needed. The Hawaiian endemic genus Tetraplasandra A. Gray as currently circumscribed contains seven species (Lowry 1990, Lowry and Wood 2000). Tetraplasandra lydgatei (Hillebr.) Harms was first described by Hillebrand (1888) as Triplasandra lydgatei; the genus Triplasandra Seem. was later subsumed into Tetraplasandra (Harms, 1898). Subsequently, Lowry (1990) combined T. lydgatei with the polymorphic, widespread species T. oahuensis (A. Gray) Harms, believing that T. lydgatei represented simply a morphological extreme in the wide range of variation encompassed among individuals of T. oahuensis. The Lowry (1990) treatment represents a more concise and workable taxonomic framework for the genus based on current data and knowledge about the ranges of species variation in the Hawaiian Islands in which many of the more than 82 species, subspecies, and varieties described in, and subsequent to, Sherff’s (1955) revision of the genus were synonymized. However, extensive field investigations by botanists John Obata and Ron Fenstemacher over many years have led them to suspect that one lowland species, T. lydgatei, still warranted taxonomic recognition based on habitat and several morphological characteristics. During my field investigations in 1995 and 1996 with Obata and Fenstemacher they identified the localities of two known Tetraplasandra individuals that they determined to be morphologically distinct from T. oahuensis. On revisiting the sites one of the two individuals had died since their last visit. The single living individual was found at an elevation of 335–340 m, which is typically lower than the usual range for T. oahuensis (>500 m) in the Ko‘olau Mountain Range of O‘ahu. In addition, the leaves of the individual were more membranous than the coriaceous leaves of T. oahuensis, but based on a single sterile individual the variation was attributed to the ecological habitat. However, in late July 1996 the plant began to flower. Even in bud the inflorescences were very distinct from those of T. oahuensis and it became clear that this was a unique species, morphologically Pacific Science (2005), vol. 59, no. 1:105–110 : 2005 by University of Hawai‘i Press All rights reserved 1 Financial support provided by the Lewis B. and Dorothy Cullman Foundation. Manuscript accepted 24 May 2004. 2 The Lewis B. and Dorothy Cullman Program for Molecular Systematics Studies, The New York Botanical Garden, Bronx, New York 10458. similar to prior scientific descriptions and type specimens of T. lydgatei. Later, senescent flowers and fruit became available for study and supplied further characters to distinguish the taxon from the other species of Tetraplasandra. The realization also struck us that the extinction of this species was imminent and the preservation of the species may require an actual resurrection rather than taxonomic resurrection. This concern spurred additional field exploration and surveys by Daniel Chun and other botanists that led to the discovery of seven additional individuals, two of which have since died. One of these flowered and fruited profusely before perishing and provided further material for this study and propagation. Currently, there are six known individuals of T. lydgatei in the southeastern Ko‘olau Mountains; I have seen three of these. Phylogenetic analyses of sequences from the nuclear ribosomal Internal Transcribed Spacer (ITS) and 5S nontranscribed spacer (Costello and Motley 2001) did not provide resolution among members of the Tetraplasandra oahuensis clade (T. oahuensis, T. lydgatei [not included in ITS], T. waimeae Wawra, and T. waialealae Rock), but this is not uncommon in closely related Hawaiian plant lineages (Ganders et al. 2000, Gemmill et al. 2002, Lindqvist and Albert 2002). The use of Amplified Fragment Length Polymorphisms (AFLP) has been useful for providing additional resolution among taxa resulting from recent and rapid species radiations (Lindqvist et al. 2003). In a recent AFLP study of the Tetraplasandra group (Costello and Motley 2003) the members of the T. oahuensis clade (plus, on the recommendation of Timothy Flynn, National Tropical Botanical Garden, an individual thought to represent T. bisattenuata Sherff [1⁄4 T. oahuensis]) formed a polytomy. One clade contained three individuals of T. lydgatei that were resolved as sister to T. waimeae and T. waialealae. A second clade included eight individuals of T. oahuensis sampled from throughout the Hawaiian Islands. The T. bisattenuata individual and a T. oahuensis individual from the Wai‘anae Mountains, O‘ahu, were unresolved. This AFLP evidence provides further support for the segregation of T. lydgatei from T. oahuensis. Morphologically it is difficult to find diagnostic characters to separate species of this clade from the polymorphic T. oahuensis without using overlapping or continuous characters. Tetraplasandra waimeae and T. waialealae are separated dichotomously from T. oahuensis in the key of the recent treatment (Lowry 1990) by their larger fruit size and inflorescences without bract scars (which occasionally do occur in T. waimeae). In the taxonomic key in the Manual of the Flowering Plants of Hawai‘i, T. lydgatei can be segregated from the other species of the genus (including T. flynnii, which was not treated) by: inflorescences strictly compound umbellate (second choice in couplet 1); rays of inflorescence with 1 to several bract scars (couplet 5[1]). This keys the species as T. oahuensis. These two species can be separated by the following couplet. Fruit cylindrical, occasionally ovoid, 7–15 mm long; leaves coriaceous; flower petals pinkish red to yellow green; nectary disk pinkish red, peduncles 3.5–10 mm wide, pedicels b1.5 mm wide; terminal umbellules of flowers flat-topped to convex, with outer pedicels progressively longer than inner ones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . T. oahuensis Fruit globose, 4–5 mm long; leaves chartaceous; flower petals always yellow to yellow green (never pink or red); nectary disk yellow; peduncles a2 mm wide; pedicels a1 mm wide; terminal umbellules of flowers spherical, with pedicels being nearly equal in length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . T. lydgatei Tetraplasandra lydgatei (Hillebr.) Harms Harms, 1898, in Engl. & Prantl, Pflanzenfam. III, 8:20; Triplasandra lydgatei Hillebr., 1888, Fl. Hawaiian Isl., p. 153. Type: ‘‘Wailupe, Isl. Oahu,’’ Rev. John M. Lydgate s.n. (holotype, formerly at b [destroyed]; isotype, bish 488665! [fragment]; possible isotype, ‘‘Niu or Wailupe,’’ Isl. Oahu, W. Hillebrand & J. M. Lydgate s.n. bish 488664!). synonomy: Tetraplasandra lydgatei var. PACIFIC SCIENCE . January 2005 106