Canadian journal of botany vol:78 issue:3 pages:288-304
The morphology and anatomy of the African monospecific genus Colletoecema E. Petit (Rubiaceae) is documented and illustrated (including wood anatomy, pollen morphology, gynoecial and exotestal structure). Morphological and anatomical comparison shows that Colletoecema differs in many aspects from the Psychotrieae (e.g., wood anatomy, seed structure). Consequently, the genus' provisional position in the Psychotrieae cannot be maintained. Morindeae, the second tribe Colletoecema has been associated with, has a different gynoecial structure. The oily endosperm and large embryo of Colletoecema is found in several genera that often were or still are included in the Psychotrieae or Morindeae (Trichostachys, Saldinia, Ronabea, and Lasianthus). However, they differ in several other aspects, which makes a close relationship doubtful. Colletoecema exhibits a unique combination of characters including axillary inflorescences, banded parenchyma in the wood, ovules attached around the middle of the septum, bilocular pyrenes, seeds with oily endosperm and large embryo, and verrucate exotestal thickenings, not encountered elsewhere in the Rubioideae. A cladistic analysis based on nucleotide sequence variation in the rps16 intron (chloroplast DNA) confirms that Colletoecema is related neither to Psychotrieae nor to Morindeae. Colletoecema appears as a sister genus of Ophiorrhiza in a weakly supported clade among the basalmost clades of the subfamily Rubioideae, but there is very little morphological support for this relationship.