Wood Anatomy of Hawaiian and New Guinean Species of Tetramolopium ( Asteraceae ) : Ecological and Systematic Aspects

Qualitative and quantitative features are reported for five Hawaiian and one New Guinean species of Tetramolopium. Tetramolopium humile differs from the other Hawaiian species in its numerous narrow vessels, numerous vasicentric tracheids, and wide rays. Although these features are adaptive in the dry alpine localities of T. humile, they would be adaptive also in the remaining species, which are from dry to moderately dry lowland localities. Thus, one can consider these features of T. humile as systematic indicators. The wood of T. pumilum (New Guinea) has distinctive wide, tall rays that may be related to the short stems in this species; T. pumilum has wood more mesomorphic than that of any of the Hawaiian species. Within Hawaiian Tetramolopium, wood anatomy correlates with dryness of habitat. The species of Tetramolopium studied have highly xeromorphic wood in comparison with woods of dicotyledons at large. Tetramolopium, A GENUS of tribe Astereae (Hoffmann 1890), has had a varied taxonomic history (see Lowrey et al. 2001). Cladistic analysis of molecular and morphological data sets (Lowrey et al. 2001) shows that Tetramolopium is polyphyletic. Most of the species are nested within Vittadinia, but T. vagans Pedley and, on a different branch, T. pumilum Mattf. are outgroups of Vittadinia. The Hawaiian species of the current study all branch from a single clade. The results of the Lowrey et al. (2001) analysis will lead to taxonomic changes. The inclusion of T. pumilum in this study offers comparisons with the wood anatomy of the Hawaiian species. Obviously, study of wood anatomy of the entire "Vittadinia group" of genera is desirable. Because the species composing this group are geographically widespread in Australia and on Pacific islands and are nonwoody, the species have not been studied hitherto except for T. I Manuscript accepted 17 June 2002. 2 Santa Barbara Botanic Garden, 1212 Mission Canyon Road, Santa Barbara, California 93105. 3 Department of Biology, University of New Mexico, Albuquerque, New Mexico 87131. Pacific Science (2003), vol. 57, no. 2:171-179 © 2003 by University of Hawai'i Press All rights reserved humile (Carlquist 1960, 1994). Some Hawaiian Tetramolopium species are extinct or very restricted in distribution (Lowrey 1986, 1990), so the assemblage of material in this study is unlikely to be bettered. The species referred to Tetramolopium are subshrubs. Wood of subshrubs is rarely collected or studied anatomically by botanists. Thus, the availability of the material studied here represents an unusual opportunity to record information on Tetramolopium wood anatomy. The wood of Tetramolopium is potentially of interest because the genus has speciated on the Hawaiian Islands (11 species, many with infraspecifically distinct populations). Most Hawaiian taxa are restricted to localities that qualify as xeric (Lowrey 1986). These habitats represent a diversity of geological and edaphic formations, ranging from alpine cinders (Haleakala, Maui) to lithified calcareous dunes (western Moloka'i). Only T. lepidotum occurs in moderately mesic sites, west-facing slopes of ridges in the Wai'anae Mountains, O'ahu (Lowrey 1986). Ecological analysis of wood anatomy of Tetramolopium is appropriate in view of the xeric nature of these sites, because wood anatomy sensitively reflects ecology in Asteraceae (Carlquist 1966). A distinction is attempted here between characters that represent direct adaptation to ecology and those that are systematic indicators regardless of ecology. The study of