Pollen morphology and phylogenetic relationship of 14 Oxalis species

Most Oxalis are highly ornamentally valuable, but their taxonomy is difficult, which greatly limits the landscape application of this genus. The pollen morphology and exine ornamentation of 14 species of the Oxalis were observed using scanning electron microscopy, and their pollen morphology was clustered and analyzed to explore their interspecific relationship based on the results of palynological clustering. The results were as follows: (1) The pollens of the 14 species observed were subspheroidal or oblatesphere, and in polar view they were all 3-colpate, of which 96.3% were medium-sized and 3.7% were small, with different style types showing the largest grains were produced in stamens with long filaments and the smallest ones in stamens with short filaments; most pollen grains were 3-colpate, sparsely 2-colpate and 4-colpate, O. stellata and O. pes-caprae, respectively; exine ornamentation could be divided into two categories: supra-areolate and reticulate. (2) For the first time, three species with aberrant pollen grains were observed, namely O. glabra, O. simplex and O. pes-caprae. The aberrant pollens exhibited as abnormal number and arrangement of the colpi, but normal exine structure. There were 2-zonocolpate grains in O. glabra, spiralaperturate grains in O. simplex, and 4-zonocolpate grains and spiralaperturate grains in O. pes-caprae. (3) The 14 species could be divided into two categories according to the exine ornamentation, one included O. massonorum and O. nidulans with supra-areolate pollen. The other category included 12 species with reticulate pollen. Species in the latter category could be further divided into four types: O. glabra, O. versicolor, and O. tenuifolia were more closely related; O. compressa, O. pes-caprae, O. namaquana, and O. fabaefolia were more closely related; O. bowiei, O. stellata, and O. perdicaria were more closely related; O. zeekoevleyensis and O. simplex were relatively distantly related to other Oxalis. The results of this study show that species with similar pollen morphology have certain similarity in plant morphology, and the pollen morphology characteristics can be used as the basis for the study of phylogenetic relationship and taxonomic classification, which can further provide a theoretical basis for the selection of parents in Oxalis cross-breeding.