The taxa of genus ~ilxora~i (Rubiaceae) occurring in Thailand were treated in detail, using both herbarium specimens and preserved material. Included are descriptions of 29 taxa, as well as information on synonyms and relevant literature, distribution ranges, phenology, vernacular names and illustrations. The 29 taxa covered include 27 species, 2 varieties and 1 subspecies. The treatment contains investigations of the habit of all taxa

leaf morphology and anatomy of selected taxa

the analysis of inflores cence structure

floral, fruit and seed morphology

palynological investigations and an analysis of the distribution patterns, with particular reference to Thailand. ~ilxora phuluangensis is a newly discovered species, and two taxa are newly recorded from Thailand (~ilxora henryi Leveille~i and~il. cambodiana~i Kurz)

~il, kratensis~i was reduced to subspecific status (~il. brunonls~iG. Don subsp. ~ikratensis~i (Craib) Chamchumroon). ~il. butterwickii~i Hole var. ~ilepida~iCraib and ~il. cibdela~i Craib var. ~ipuberula~i Craib are new syno nyms of ~il. butterwickii~iand ~il. cibdela~i, respectively. Eleven species (plus several varieties and cultivars) of~ilxora~i grown in Thailand as ornamentals are also dealt with, and an identification key tothem. The analysis of the distribution pattern of ~ilxora butterwickii~i on Doi ChiangDao using the Index of Dispersion (I(,(+,d)) revealed contagious distribution with intra-clump distribution being uniform. Also included is a study on reproductive ecology of ~il. buttenvickii~i. Both are significant for and contribute to a betterunderstanding of conservation of the mountain. A morphological cladistic study partly supported the infrageneric classification of Thai Ixoras into two groups, namely subgenus Ixora ('Eu-Ixora'

the main group) and subgenus Pavettioides (the minor group).