Elasmostemon E.M.FRIIS, P.R.CRANE, K.R.PEDERSEN, M.M.MENDES et J.KVAČEK, 2022

Friis, Else Marie, Crane, Peter R., Pedersen, Kaj Raunsgaard, Mendes, Mário Miguel & Kvaček, Jiří, 2022, The Early Cretaceous Mesofossil Flora Of Catefica, Portugal: Angiosperms, Fossil Imprint 78 (2), pp. 341-424 : 375

Genus Elasmostemon E.M.FRIIS, P.R.CRANE, K.R.PEDERSEN, M.M.MENDES et J.KVAČEK gen. nov.

T y p e. Elasmostemon paisii E.M.FRIIS, P.R.CRANE, K.R.PEDERSEN, M.M.MENDES et J.KVAČEK gen. et sp. nov.

P l a n t F o s s i l N a m e s R e g i s t r y N u m b e r.

PFN0002792 (for new genus).

E t y m o l o g y. From Greek elasma for lamina and stemon for stamen.

G e n e r i c d i a g n o s i s. Stamen laminar. Anthers tetrasporangiate, dithecate. Thecae positioned close to the stamen margin and separated by a massive, broad connective. Stamen apex rounded without an apical extension. Dehiscence longitudinal. Staminal tissue with larger cells, probably ethereal oil cells. Pollen monocolpate, circular in equatorial view, semitectate-reticulate. Reticulum loosely attached, heterobrochate. Aperture long, reaching the equator, with distinct margins. Columellae short.

C o m m e n t s o n t h e g e n u s. The broad and flattened stamen and monoaperturate pollen strongly suggest a position among basal grade angiosperms. Laminar or laminar-like stamens that have pollen sacs positioned at, or close to, their margin occur among some extant ANA-grade angiosperms ( Austrobaileya C.T.WHITE and Nymphaeaceae ) and Magnoliales , and ethereal oil cells like those seen in the fossil stamens are also present in stamens of Austrobaileya and Magnoliales (e.g., Canright 1952, Endress and Hufford 1989). Stamens of Austrobaileya are flattened as in the Catefica fossils and Austrobaileya pollen is also reticulatecolumellate. However, in Austrobaileya the two thecae are close together on either side of the mid-line of the stamen with little connective tissue between them ( Canright 1952, Endress and Hufford 1989). Pollen of Austrobaileya is also much larger, between 51 and 100 µm, than the pollen of the Catefica material ( Halbritter 2016). Stamens of Nymphaeaceae lack oil cells and the pollen is non-reticulate and often zona-aperturate (see discussion of “Stamen with zona-aperturate pollen” above).

In Magnoliales stamens of Degeneria I.W.BAILEY et A.C.SM. (Degeneriaceae) and Galbulimima F.M.BAILEY (Himantandraceae) are broad as in the Catefica stamen, but pollen in Degeneria is psilate with granular infratectal layer and pollen in Galbulimima is atectate ( Endress and Hufford 1989). Eupomatia (Eupomatiaceae) also has laminar-like stamens, but the pollen is zona-aperturate. In Magnoliaceae , the thecae are laminar or marginal and pollen is typically psilate. Semitectate-reticulate pollen is known among other Magnoliales , including species of Horsfieldia WILLD. , Myristicaceae ( Sauquet and Le Thomas 2003) and several Annonaceae ( Walker 1971) , but stamens in these two families are not laminar.