Evolution of succulent Euphorbia,/i> as interpreted from latex composition

Abstract

The morphology of starch grains and the gas-liquid chromatographic profile of triterpenes derived from latex of the nonarticulated laticifer of succulent African  Euphorbia were examined for their applicability to interpret phylogenetic relationships of this genus. Several trends in starch grain morphology and triterpene composition were evident in the 38 examined taxa. Rod shaped grains, interpreted to be conservative, occurred in only a few taxa in several dwarf groups. Grains of osteoid shape prevailed in most taxa. Highly osteoid grains possessing lobed ends represented the most complex form and were present in some taxa endemic to Madagascar. Triterpene profiles which contained from 2 to 14 or more compounds were derived from all taxa. Each taxon possessed a characteristic profile, or identifying fingerprint. The composition of the profile differed quantitatively and qualitatively among taxa. Taxa with few triterpenes, tentatively interpreted as primitive, occurred in dwarf forms, whereas Madagascan taxa tended to possess high numbers of triterpenes reflective of specialization. This study supports the interpretation that laticifer starch grain morphology and triterpene composition, both gene mediated stable markers, can be employed to determine and correlate phylogenetic relationships between taxa of this complex genus.