Proencistemon 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 : 353

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

Type. Proencistemon portugallicus E.M.FRIIS, P.R.CRANE, K.R.PEDERSEN, M.M.MENDES et J.KVAČEK gen. et sp. nov.

Plant Fossil Names Registry Number.

PFN002788 (for new genus).

Etymology. In honor of Pedro Proença e Cunha for his contributions to understanding the stratigraphy and geology of the Early Cretaceous of Portugal and stemon (Greek for stamen).

G e n e r i c diagnosis. Staminate inflorescences spherical with closely packed, unisexual flowers radiating from the central axis. Each flower delimited by a bract subtending one or two stamens. Anthers sessile, or almost sessile, narrowly elongate, dithecate and tetrasporangiate, lacking a well-developed filament but with a short flattened apical connective. Anther dehiscence lateral by longitudinal slits. Pollen small, trichotomocolpate, circular in outline, semitectate-reticulate, columellate, with long, scattered columellae and a homobrochate reticulum. Muri with a rounded profile and supratectal ornamentation composed of minute verrucae aligned in two to three longitudinal rows that create poorly defined transverse ridges over the muri. Aperture margin indistinct. Aperture membrane irregularly verrucate. Orbicules spherical with fine verrucate-spiny ornamentation.

Distinguishing features. Among extant angiosperms, species of Ascarina (Chloranthaceae) are comparable to Proencistemon in having staminate inflorescences consisting of simple flowers with one to three stamens. Pollen grains of extant Ascarina , as well as extant Hedyosmum , are also closely similar to those found in situ in Proencistemon . The grains have an indistinctly delimited polar aperture with poorly defined aperture margins, an aperture membrane covered by irregular verrucae, and a semitectate-reticulate pollen wall with finely beaded supratectal ornamentation. The trichotomocolpate pollen of Proencistemon is most similar to the monocolpate or sometimes trichotomocolpate pollen of Ascarina . Pollen of Hedyosmum is pentachotomocolpate or more rarely tetra-or hexachotomocolpate. Proencistemon flowers also differ from those of Hedyosmum in being delimited by a bract. In extant Hedyosmum the flowers are ebracteate and presumed to be unistaminate.

There are several records of staminate inflorescences, inflorescence fragments and isolated stamens from the Early Cretaceous of Portugal that are similar to Proencistemon and that also contain chloranthoid pollen, but so far none of them has been named. Hedyosmum -like staminate inflorescences from the Torres Vedras locality ( Friis et al. 2019a: text-fig. 20h) and from the Vale de Água locality (Friis et al. 2011: figs 8.13D, E, 16.2B) that have five whorls of staminate flowers differ in being ebracteate with smaller stamens, and have a larger number of stamens in each whorl than in Proencistemon . In addition, while the form of the pollen aperture in the single Torres Vedras specimen of a Hedyosmum -like staminate inflorescence is unknown, it is tetra- to pentachotomocolpate in the Vale de Água specimen. The tetra- to pentachotomocolpate pollen grains of the Vale de Água specimen are comparable to grains of Hedyosmum and to dispersed grains assigned to the extinct pollen genus Asteropollis . In contrast, Proencistemon has trichotomocolpate pollen. Although trichotomocolpate pollen grains are sometimes assigned to Asteropollis , the type material for Asteropollis asteroides R.W.HEDL. et G.NORRIS from the Early Cretaceous (Albian) of Oklahoma, USA, only includes forms with pentachotomocolpate, or rarely tetrachotomo- or hexachotomocolpate apertures. Trichotomocolpate grains are not recorded from the type locality ( Hedlund and Norris 1968).

Fossil pollen grains with a trichotomocolpate aperture similar to that of Proencistemon have sometimes been assigned to the extinct pollen genus Clavatipollenites C OUPER ( Doyle and Robbins 1977) or treated as aff. Clavatipollenites ( Walker and Walker 1984) . Dispersed trichotomocolpate pollen grains from the Early Cretaceous (Aptian) of Patagonia described as Jusinghipollis ticoensis M.LLORENS et LOINAZE ( Llorens and Perez Loinaze 2015) are closely similar to the in situ pollen of Proencistemon , but the reticulum is looser, the muri are narrower, and the ornamentation of the tectum is coarser. The type species of Jusinghipollis JANSON. et HILLS, J. microreticulata (JUHÁSZ et GÓCZÁN) JANSON. et HILLS, which is based on dispersed pollen from the Albian of Hungary ( Juhász and Góczán 1985), also has a trichotomocolpate aperture, but differs from pollen of Proencistemon in having longer aperture arms that almost reach to the equator. The aperture margins are also more well defined than the diffuse aperture margins in Proencistemon pollen grains.