Quadrispermum parvum E.M.FRIIS, K.R.PEDERSEN et P.R.CRANE, 2013

Friis, Else Marie, Crane, Peter R. & Pedersen, Kaj Raunsgaard, 2019, The Early Cretaceous Mesofossil Flora Of Torres Vedras (Ne Of Forte Da Forca), Portugal: A Palaeofloristic Analysis Of An Early Angiosperm Community, Fossil Imprint 75 (2), pp. 153-257 : 171-173

Quadrispermum parvum E.M.FRIIS, K.R.PEDERSEN et P.R.CRANE, 2013

Text-fig. 11b, c, g

D e s c r i p t i o n a n d r e m a r k s.Chlamydospermous seeds that are four-angled to circular in transverse section, about 1.1 mm long and 0.6 mm wide. The seed envelope is sclerenchymatic with irregular transverse ridges extending between the corners of the seed envelope ( Text-fig. 11b, c ). The seed envelope is extended into a pointed micropylar protrusion that is surrounded by a shallow depression ( Text-fig. 11b, c, g ). No pollen grains have been observed in the micropyle, but monocolpate pollen grains have been observed in the micropylar region of one seed ( Text-fig. 11g –i ) and on the surface of two other seeds. The pollen grains are about 13 µm long, with a long colpus that extends for almost the full length of the grains. The tectum has a distinctive surface ornamentation formed by a delicate pattern of fine, interwoven elements.

A f f i n i t y a n d o t h e r o c c u r r e n c e s. Quadrispermum parvum is common in the Torres Vedras mesofossil flora, and is also recorded from the Arazede, Catefica, Famalicão, and Vale de Água localities in Portugal. The species is also common in the Puddledock mesofossil flora from Virginia, USA ( Friis et al. 2013). The distinctive chlamydospermous structure of the seeds indicates a relationship to the Bennettitales-Ertmanithecales-Gnetales group of Friis et al. (2009).

The pollen associated with Quadrispermum has not been linked to other plants in the mesofossil floras from Portugal. It is currently the only pollen type associated with Quadrispermum and it is therefore possible that these grains were produced by the Quadrispermum -plant. The pollen grains are similar to those figured by Hughes and McDougall (1994) as “Small Berriasian monosulcate, with apparently fibrous sexine” from the Worbarrow borehole, Dorset, England, from sediments now dated as of Hauterivian age (Hughes 1994). Among extant plants somewhat similar pollen is known for Ginkgo biloba L., but pollen grains of Ginkgo are much larger (about 30–48 µm long; Korszun and Klimko 2014) than the grains found on the Quadrispermum seeds. A similar interwoven tectum ornamentation is also known for grains found in situ in the Jurassic presumed cycadaceous pollen cone Androstrobus szei T.M.HARRIS ( Hill 1990) , but these grains are also much larger than those from Torres Vedras.

Figures

Text-fig. 11. Scanning electron microscope (SEM) images of seeds assigned to the BEG group (a–d) and associated pollen grains (e–i); Torres Vedras locality, Portugal. a) Seed of Tomcatia taylorii showing the four horns formed by extensions of the envelope and the central projection of the envelope that surrounds to the micropylar tube; b, c) Seeds of Quadrispermum parvum in lateral (b) and apical (c) views showing the transverse ribs and the central projection of the envelope that surrounds the micropylar tube; d–f) Seeds of Ephedrispermum lusitanicum showing the four-angled seed envelope (d), the micropylar tube surrounded by the tissues of the integument (e), and ephedroid pollen grains on the seed surface (f); g) Apex of seed of Quadrispermum parvum showing simple