Diversity, development and systematic significance of seed pedestals in Scrophulariaceae (s.l.)
Rebernig, Carolin A.; Weber, Anton
published: Dec 6, 2007
Whereas seed features of Scrophulariaceae (in their traditional circumscription) have been well studied and used as a taxonomic marker, little attention has been paid to how the seeds are attached to the placenta. The structures supporting the seeds are usually referred to as seed funicles, but study of development shows that they develop from the placenta and are not part of the ovule. In case of seed abortion, the seed funicle is usually fully developed and thus reveals its morphological independence from the seed. Therefore, we here use the term seed pedestal instead of seed funicle. The seed pedestals exhibit a surprising variation and diversity within Scrophulariaceae. In the present survey, based on a SEM study of 45 species out of 27 genera, 5 types of seed pedestals (plus one of complete lack) were found. Partly, they prove of considerable systematic interest. Thus a new field of micromorphology is opened that may provide new and valuable characters for assessing or confirming affinities. Time is not ripe to draw far-reaching conclusions (traditional Scrophulariaceae, as treated by Fischer 2004, include more than 300 genera, and studies on a broad scale are badly needed), but there are promising signs: unique pedestal types occur in Paulownia (and thus support the recent ranking as a family of its own) and in Penstemon (a genus of tribe Cheloneae in the recently dramatically expanded Plantaginaceae, but outstanding by the presence of pair-flowered cymes). The conspicuous Manulea-type (collar-shaped pedestals) is predominantly found in the South African tribe Manuleae and other genera from the Cape region (thus strongly suggesting a closer affinity), and occurs also in Scrophularia (all belonging to Scrophulariaceae s.str.). The Digitalis-type is found both in Scrophulariaceae s.str. and Plantaginaceae s.l. and possibly represents a rather ancestral type. So it is not surprising to find it also in Calceolaria, which was recently raised to family rank and placed in basal Lamiales. Random samples of 11 other (mainly advanced) families of Lamiales were examined, but no seed pedestals were found. However, their occurrence in Calceolariaceae and Tetrachondraceae shows that such structures may occur here and there in (especially basal) families of the order.