Aristospermum huberi E. M. FRIIS, P. R. CRANE et K. R. PEDERSEN 2022

Aristospermum huberi E. M. FRIIS, P. R. CRANE et K. R.PEDERSEN, 2022

Text-fig. 19a–c

Description and remarks. Seeds strongly flattened, triangular in outline, about 1.9 mm long and 1.65 mm broad (Text-fig. 19a). The seeds are anatropous and bitegmic with an outer integument (testa) consisting of an outer layer (exotesta) of thin-walled cells and an inner layer (endotesta) of crystalliferous cells. The exotesta is typically abraded and preserved only in patches along the margins of the seed where the abraded palisade-shaped cells form an irregular border around the rest of the seed (Text-fig. 19a). The endotesta is one cell layer deep and each cell has one, or more rarely two, large crystals, which are seen as one or two angular imprints in the center of the cell (Text-fig. 19a–c). The inner integument (tegmen) has two layers of elongated fiber cells that are arranged perpendicular to each other (Text-fig. 19c) and an inner layer of small cubic cells. The micropyle is formed from the inner integument. A narrow funicle extends along one margin of the seeds, but it is often only partly preserved (Text-fig. 19a).

Affinity and other occurrences. The anatomy of the seed coat of these seeds strongly suggests a relationship to extant Aristolochiaceae, including Aristolochia L., which has very similar triangular and flattened seeds with a bitegmic seed coat. In extant Aristolochiaceae the testa, which forms from the outer integument, consists of an outer layer of thin-walled cells and an inner layer of crystalliferous inner cells. The tegmen, which forms from the inner integument, consists of two layers of fibrous cells that are more or less perpendicular to each other and an inner layer of cubic cells (Corner 1976). These details of the seed coat are unique for the family (Corner 1976, González and Rudall 2003) and justify the conclusion of a close relationship between these fossils and extant Aristolochiaceae. However, the combination of features seen in the fossil material, including the course of the raphe, exclude assignment of the fossil seeds to any extant genus of the Aristolochiaceae (Friis et al. 2022).

Similar aristolochiaceous seeds are also present in other Early Cretaceous mesofossil floras from Portugal and North America including specimens in which the outer tissues are better preserved. The formal description of the species is based on an assessment of that broader suite of specimens, including the type material from the Buarcos mesofossil flora (Friis et al. 2022).