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Contribution to the knowledge of the pollen morphology in the tribe Orobancheae Lam. & DC. (Orobanchaceae)

Coutinho, António Pereira, Silveira, Paulo Cardoso Da, Portugal, António, Albuquerque, Joana Isabel, Pujadas-Salvà, Antonio J.
Grana 2019 v.58 no.1 pp. 14-44
Cistanche, Orobanche cernua, light microscopy, pollen, principal component analysis, scanning electron microscopy
The pollen grains of 53 species and 57 taxa of two genera (Cistanche, Orobanche s. l.) of tribe Orobancheae were studied with light microscopy (LM). Thirty-five of these species were also studied with scanning electron microscopy (SEM). Two pollen types (Orobanche and Phelipanche) and six pollen groups (I–VI) were described. A principal component analysis was performed to help clarify some taxonomic problems at generic, specific and infraspecific levels. Some transition forms exist between the two pollen types. We consider that these data support the elevation of Trionychon to the rank of subgenus (Phelipanche). The pollen morphology of the subgenus Boulardia and of the genus Cistanche is quite similar to that of subgenera Orobanche and Phelipanche, respectively. Our results support the position of Boulardia as the sister taxon to Orobanche s. s. The contribution of pollen morphology to the resolution of several taxonomic problems related to specific and infra-specific taxa was discussed. Within the Orobancheae, the tricolpate, isopolar, microreticulate-scabrate pollen grains are plesiomorphic and the apolar, granulate, inaperturate pollen grains are apomorphic. Some taxa (e.g. O. cernua, O. cumana, O. lavandulacea and O. mutelii) present pollen heteromorphism, which could be related to the existence of geographical clines. The polymorphic (inaperturate, colpate), scabrate-perforate, tectate-columellate pollen grains present in some species (O. cernua, O. cumana) possibly represent an intermediate evolutionary type. Considering the separation of specific and infraspecific taxa in the Orobancheae, LM is apparently more useful than SEM, although information from SEM is clearly relevant as a complement for LM.