Pyrene and pollen observations in the pantropical genus Geophila (Rubiaceae‐Psychotrieae)

Abstract

Pyrene and pollen morphology of several neo‐ and paleotropical Geophila species is documented and discussed. Pyrenes show distinct morphological variation. They have one central or several adaxial ribs and are straight or twisted. Neotropical species only have twisted pyrenes, whereas Madagascan species have straight ones. Both pyrene types occur on the tropical African mainland and in tropical Asia. The genus is eurypalynous, including inaperturate, colpate and pantoporate pollen. The paper includes the first record of operculate pollen in the Rubiaceae, viz. in Geophila repens var. repens. Pyrenes as well as pollen morphology indicate that the varieties of the pantropical species G. repens need recognition at the specific level.

Gomphocalyx and Phylohydrax (Rubiaceae): sister taxa excluded from Spermacoceae s.s., featuring a remarkable case of convergent evolution

“…The subshrubby habit of Lathraeocarpa is also much closer to the shrubby habit of Triainolepis than to the herbaceous habit of Gomphocalyx. The fusion of Lathraeocarpa and Gomphocalyx as proposed by Piesschaert (2001) is not corroborated by our current knowledge. Once more, we will have to wait until molecular data become available to determine the position of Lathraeocarpa more confidently.…”

“…The main reason for questioning a relationship between Gomphocalyx and Lathraeocarpa is that the ovary of the latter genus is tetralocular. Furthermore, the fruits of Lathraeocarpa are fleshy and not dry as in Gomphocalyx, and in Lathraeocarpa decaryi Bremek., the pyrene is surrounded by eight strands of thin-walled cells, very similar to the fruit wall anatomy observed in some Triainolepis species (see Bremekamp, 1957;Piesschaert, 2001). The subshrubby habit of Lathraeocarpa is also much closer to the shrubby habit of Triainolepis than to the herbaceous habit of Gomphocalyx.…”

“…In the following paragraphs, we identify characters that do in fact indicate (1) a close relationship between Phylohydrax and Gomphocalyx and (2) their new position amidst former Hedyotideae genera. We also discuss the synonymy between Lathraeocarpa and Gomphocalyx as proposed by Piesschaert (2001).…”

“…In Geophila repens (L.) I. M. Johnst., however, a genus belonging to the same tribe, up to 150 pores were counted (Piesschaert & al., 1999;Vanthournout, 2002). In the Hedyotideae-Hedyotis group, several genera show a tendency to develop more than three apertures.…”

“…This position seems supported by the pluri-zonocolporate pollen grains and uni-ovulate locules of Gomphocalyx. Capuron (1973), however, supposed a relationship with the monogeneric tribe Lathraeocarpeae, and Piesschaert (2001) even proposed merging Lathraeocarpa Bremek. with Gomphocalyx.…”