Proencistemon portugallicus E. M. FRIIS, P. R. CRANE, K. R. PEDERSEN, M. M. MENDES et J. KVACEK 2022, sp. nov.
Creators: name: Friis, Else Marie
name: Crane, Peter R.
name: Pedersen, Kaj Raunsgaard
name: Mendes, Mário Miguel
name: Kvaček, Jiří
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Plantae
Tracheophyta
Magnoliopsida
Chloranthales
Chloranthaceae
Proencistemon
Proencistemon portugallicus

description: Proencistemon portugallicus E.M.FRIIS, P.R.CRANE, K.R.PEDERSEN, M.M.MENDES et J.KVAČEK sp. nov.
Text-figs 8a–f, 9a–g
Holotype. P0341 (Catefica sample MM282; figured Text-fig. 8a, c, d).
Plant Fossil Names Registry Number.
PFN002789 (for new species).
Paratypes. S266015, S266016 (Catefica sample 49), S170393, S170394 (Catefica sample 50), S174257 (Catefica sample 150), S122086 (Catefica sample 342).
Repository. Holotype: Geological Museum of Lisbon, Portugal (P).
Paratypes: Palaeobotanical Collections, Department of Palaeobiology, Swedish Museum of Natural History, Stockholm, Sweden (S).
Etymology. From Portugal where the fossils were recovered.
Type locality. Catefica (39° 03ʹ30ʺ N; 09°14ʹ 30ʺ W), between the villages of Catefica and Mugideira, about 4 km south of Torres Vedras, Portugal.
Type stratum and age. Almargem Formation, Early Cretaceous (Aptian-early Albian).
Specific diagnosis. As for the genus with the following addition: anthers very narrowly elliptical and of the same width from base to apex.
Distinguishing features. Proencistemon portugallicus is distinguished from the staminate inflorescence fragment from Catefica described here as Proencistemon sp., in having shorter stamens in which the pollen sacs are of equal width from base to apex. In Proencistemon sp. the pollen sacs are broader towards the apex.
Dimensions. Staminate structure (measured on holotype) about 1.5 mm in diameter; stamens 0.55 mm long and 0.25 mm broad; pollen diameter 12.5–16 µm.
Description and remarks. The material includes two spherical staminate inflorescences that are three dimensionally preserved and have several series of stamens radiating from the central axis (Text-fig. 8a, b). There are also strongly compressed, lignitised inflorescence fragments (Text-fig. 9a, b), isolated stamens and pollen clumps. The inflorescences are unisexual, about 1.5 mm in diameter and appear to be more or less spherical. They consist of up to 30 densely packed stamens. Bracts observed on the abaxial surface of an inflorescence fragment are poorly preserved (Text-fig. 9a) and it is unclear whether each bract subtends one or several stamens. The arrangement of the stamens in the three-dimensionally preserved specimens is also not conclusive. In specimen P0341 stamens appear to be arranged singly (Text-fig. 8a), while in specimen S174257 some of the stamens appear to occur in pairs (Text-fig. 8b). This is also the case for several of the compressed specimens (Text-fig. 9a, b).
Stamens are narrowly elongate, elliptical to rectangular in shape, about 0.55 mm long, 0.25 mm broad, and lack a well-developed filament. Anthers are sessile or almost sessile, dithecate, tetrasporangiate and with a short flattened apical connective that is mostly abraded (Text-fig. 8a, b). Stamens in the lignitised specimens are flattened and elliptical (Text-fig. 9b). They are slightly longer than those in the charcoalified stamens, but are treated here as the same species based on the identical pollen. Pollen grains are small, circular in outline, 12.5–16 µm in diameter and have a trichotomocolpate aperture in which the arms are short and do not reach to the equator (Text-figs 8c, e, 9c–f). The aperture margin is indistinct and the aperture membrane is irregularly verrucate (Text-figs 8c, e, 9c–f). The pollen wall is semitectate-reticulate with a homobrochate reticulum (Text-figs 8c–f, 9c–f). Muri are about 0.2 µm broad with a rounded profile and a supratectal ornamentation of minute verrucae that are aligned in two to three longitudinal rows and form poorly defined transverse ridges over the muri (Text-figs 8d, f, 9g). Muri are supported by medium sized and widely spaced columellae (Text-figs 8d, 9g). Lumina are irregular in shape and up to about 0.8 µm in diameter. Tiny, spherical orbicules, about 0.5 µm in diameter, which are ornamented by fine verrucae-spinules, are present on the surface of some pollen grains (Text-fig. 8f). Pollen morphology and ultrastructure was described in detail for specimen P0341 (Tekleva et al. 2021), which we designate here as the holotype of Proencistemon portugallicus.
Affinity and other occurrences. For comments on the relationships to extant chloranthoids see discussion of the new genus above. A phylogenetic analysis was performed by Tekleva et al. (2021) based on specimen P0341, which suggested that “despite some uncertainty … phylogenetic analyses are most consistent with a position attached to the stem lineage of Hedyosmum.” This conclusion may be correct, but because other relevant specimens were not considered, the full significance of the material requires further analysis. In specimen P0341 the bracts are not obvious and the stamens appear to be borne singly. The flowers were therefore interpreted as ebracteate and unistaminate (Tekleva et al. 2021). However, in another specimen bracts are clearly present (Text-fig. 9a), and in several inflorescence fragments stamens appear to occur in pairs (Text-figs 8b, 9a). Together with the trichotomocolpate pollen, these points of similarity with extant Ascarina, rather than with extant Hedyosmum, need to be considered.
Densely crowded stamens very similar to those of Proencistemon portugallicus, and also with similar in situ trichotomocolpate pollen, have been described from the Torres Vedras mesofossil flora (Friis et al. 2019a: text-fig. 21). The two taxa are clearly closely related, but stamens of the Torres Vedras specimens are larger and more crowded and also have larger pollen grains (about 18–22 µm in diameter compared to 12.5–16 µm in diameter in Proencistemon portugallicus). Whether the stamens in the Torres Vedras specimens are in pairs, and whether the flowers were bracteate or ebracteate is unknown.
In the Catefica palynoflora similar trichotomocolpate pollen grains are rare, but have been reported from coastal exposures in Portugal that are of Early Cretaceous age as Asteropollis cf. asteroides, Asteropollis sp. 3 and Asteropollis sp. 4 (Heimhofer et al. 2007). These trichotomocolpate grains are similar to those of Proencistemon portugallicus in general morphology, but are larger. The specimen illustrated and assigned to Asteropollis as Asteropollis cf. asteroides (Heimhofer et al. 2007: pl. III, figs 1, 2) differs more significantly in being tetrachotomocolpate.
description: Published as part of Friis, Else Marie, Crane, Peter R., Pedersen, Kaj Raunsgaard, Mendes, Mário Miguel & Kvaček, Jiří, 2022, The Early Cretaceous Mesofossil Flora Of Catefica, Portugal: Angiosperms, pp. 341-424 in Fossil Imprint 78 (2) on pages 355-357, DOI: 10.37520/fi.2022.016, http://zenodo.org/record/7522801