POLLEN MORPHOLOGY, EXINE STRUCTURE AND THE RELATIONSHIPS OF BASELLACEAE AND DIDIEREACEAE TO PORTULACACEAE

The pollen of Basellaceae and Didiereaceae, two of the 12 traditional families comprising the Caryophyllales, was investigated using light m icroscopy, scanning and transmission electron microscopy to clarify re lationships between these two families and three others, Portulacaceae , Cactaceae, and Hector-ellaceae. These five families constitute the s uborder Portulacineae. The pollen characteristic that unites the Caryo phyllales is a spinulose tectum having annular perforations or punctae . Basellaceae, comprising four genera and 19 species, have pollen that is mostly pantocolpate with variable tecta. Pollen of Anredera has a spinulose and annular perforate or punctate tectum, an apertural endex ine with a solid inner component, and foot layers subtended by threadl ike non-apertural endexines. Basella alba has cube-shaped grains with one colpus in each of six large, thin-walled apertural fields, and a r eticulate tectum. Pollen of the three species of Basella endemic to Ma dagascar, B. excavata, B. leandriana and B. madagascariensis, is subcu boidal with apertures similar to B. alba but has deeply punctate tecta notably lacking spinules. Pollen of Basella paniculata is 12-15 panto colpate and has a spinulose and punctate tectum; it is the only specie s of Basella to have pollen more typical of the order. Tournonia is th e only genus of Caryophyllales to have pollen with thickened foot laye r around each small pore. Pollen of Didiereaceae, a family comprising four genera and 11 species endemic to Madagascar, is more uniform than that of Basellaceae. All members of Alluaudia, Alluaudiopsis, Decaryi a, and Didierea have 5-7-zonocolpate pollen with echinate or spinulose aperture membranes, and spinulose and annular perforate tecta. The tw o species of Alluaudiopsis have pollen with a unique endexine of verti cal strands and columellae that become fimbriolate near the tectum. Po llen of nine species of Portulacaceae, representing Calandrinia, Cerar ia, Grahamia, Montiopsis, Naiocrene, Talinella and Talinum, was also e xamined and is illustrated in scanning and transmission electron micro graphs. Some species of Portulacaceae have pollen with irregular and/o r perforated foot layers and threadlike non-apertural endexines that a re very similar to some Basellaceae (Anredera). Some members of Basell aceae, of Didiereaceae and of Portulacaceae, share exines with partial ly fused columellae, granular inner surfaces, and columellae narrowed near the middle or expanded near the base. However, all characteristic s may not be present in pollen of one species, and there could be spec ies of Portulacaceae with pollen having none of the above structural c haracteristics. Pollen of some members of Cactaceae, examined in an ea rlier study, has similar structural characteristics. These shared poll en characteristics provide support for the present concept of the subo rder Portulacineae. The presence of the above structural characteristi cs in pollen of Portulacineae does not necessarily deny their existenc e in pollen of the remaining members of Caryophyllales.