Seed characters in Molluginaceae (Caryophyllales): implications for taxonomy and evolution

Molluginaceae include c. 90 species distributed worldwide. The circumscription and intrafamilial relationships were recently re-evaluated after molecular investigations, but the seed characters and their evolutionary trends are poorly known. Seeds of 76 species from all 11 genera of Molluginaceae were studied. Fourteen morphological and anatomical seed characters were analysed, with further conclusions for characterization of the genera or major clades in the family. Pharnaceum in its recent circumscription is carpologically heterogeneous, and all seed characters of P. namaquense and P. pusillum, which were transferred into this genus based on the morphological similarities, indicate their placement in Hypertelis. The generic placement of P. serpyllifolium is also ambiguous. The evolutionary history of all 14 characters under consideration was reconstructed using phylogenetic analysis, and the ancestral seed characters of Molluginaceae are described. The Polpoda - Adenogramma + Psammotropha subclade is the only lineage in which the one-seeded fruits evolved. The loss of the stalactites in the outer walls of the testa cells seems to be connected with the reduction in the testa thickness. Kewa (Kewaceae, previously included in Hypertelis) shares many carpological homoplasies with Molluginaceae. The seed traits in the 'globular inclusion' clade (core Caryophyllales) are briefly discussed, and Molluginaceae are compared with other representatives of the clade. Among the taxa of the 'globular inclusion' clade with multi-seeded fruits, the smallest seeds have evolved in some genera of Molluginaceae and Aizoaceae.