The evolutionary patterns of the plant family Amaranthaceae on the Galapagos and Hawaiian Islands

ELIASSON, U. H. (Botanical Institute, Goteborg University, Box 461, SE 405 30 Goteborg, Sweden). The evolutionary patterns of the plant family Amaranthaceae on the Galapagos and Hawaiian Islands. J. Torrey Bot. Soc. 131:105-109. 2004-Different subfamilies of the Amaranthaceae have differentiated in the Galapagos and the Hawaiian Islands. In both archipelagos the endemic taxa exhibit a wide range of variation. Woodiness has evolved in both archipelagos through the so-called anomalous secondary growth typical of the caryophylliid families. Hybridization and transgression phenomena probably play an important role and may explain the morphological variation patterns in some taxa. Variation within individual populations sometimes hint to incipient speciation. In the Galapagos the subfamily Gomphrenoideae is represented by endemic species of Alternanthera, Lithophila and Blutaparon. Morphological features suggest that the group of about nine endemic species of Alternanthera can be traced back to two or three original colonization events. Several infraspecific taxa have been recognized but the current classification should be regarded as tentative and further studies based on molecular data are needed. In the Hawaiian Islands the subfamily Amaranthoideae has differentiated, with one genus, Nototrichium, endemic with three species. The genus Charpentiera has five endemic species in Hawaii and one species in the Austral Islands. The higher level of endemism in Hawaii as compared with that in the Galapagos stems from the combined effects of the more isolated geographical position, the more varied ecological conditions, and the greater geological age of the Hawaiian chain.