Elasmostemon paisii 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 : 376-378

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

Text-figs 25a–h , 26a–c

Holotype. S105281 (Catefica sample 151; figured Text-fig. 25d–h ).

Plant Fossil Names Registry Number.

PFN002793 (for new species).

Paratypes. S115859, S172560 (Catefica sample 49).

Repository. Palaeobotanical Collections, Department of Palaeobiology, Swedish Museum of Natural History, Stockholm, Sweden (S).

Etymology. In honor of Professor João Pais (1949 – 2016) for his contribution to the palaeobotany and geology of Portugal.

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.

Dimensions. Stamen fragments 0.6–1.7 mm long (full length unknown); 0.5–0.7 mm broad.

Description and remarks. The material comprises two small stamen fragments (S105281 and S115859) that are about 0.6–0.8 mm long and 0.5 mm broad ( Text-fig. 25a, d ) and a larger fragment (S172560), about 1.6 mm and 0.7 mm broad ( Text-fig. 26a–c ). The three fragments preserve different parts of the stamen, and apparently also slightly different developmental stages. They are treated here as a single species based on the stamen shape, the orientation and positioning of the narrow pollen sacs, and the shared in situ monocolpate, semitectatereticulate pollen ( Text-figs 25a–h , 26a–c ).

The stamens are broad, tetrasporangiate and dithecate, and abaxially-adaxially flattened. The stamen apex, preserved in specimens S115859 and S172560, is rounded without an apical extension ( Text-figs 25a , 26a ). The stamen base is not preserved in any of the specimens and the full length of the stamen is unknown. In specimen S115859 the marginal tissue appears to be abraded. The pollen sacs are arranged in two pairs on one surface of the stamen close to the stamen margins. It is unknown whether the pollen sacs are on the abaxial or adaxial stamen surface. The two pairs of pollen sacs are separated from each other by a broad zone of connective tissue but are oriented such that they converge and meet near the stamen apex ( Text-fig. 25a, d ). Dehiscence of the pollen sacs is longitudinal. In the two smaller fragments the thecae are not open, while in the larger specimen the thecae are dehisced with their walls curved back ( Text-fig. 26a ). Larger cells, interpreted as ethereal oil cells, are closely spaced in the staminal tissue and particularly well-preserved in specimen S115859 as shallow depressions surrounded by several cells that produce rounded swellings ( Text-fig. 25a, b ). In the other two specimens these cells are obscured by poor preservation.

Mature pollen grains are exposed by fractures in the undehisced, smaller specimens. In the larger, dehisced specimen most of the pollen had been shed, but a group of grains, perhaps immature, remained attached to the inside of the anther wall. Pollen grains of specimen S115859 were described and figured earlier as Pollen type D.8 ( Friis et al. 1999). Grains from specimen S105281 are very similar but folded, which obscures the apertures. The pollen is circular in equatorial view, about 15–17 µm in diameter, and monocolpate. The exine is semitectate-reticulate with a heterobrochate, loosely attached reticulum ( Text-fig. 25c, e–h ). The aperture is long, reaches to the equator, and has distinct margins ( Text-fig. 25e ). Lumina are rounded to angular, with larger lumina up to about 1.6 µm in diameter and smaller lumina about 0.2–0.5 µm in diameter. Muri are narrow, about 0.2 µm wide, with a flattened profile and smooth surface ( Text-fig. 25h ). Columellae are short, about 0.2 µm long ( Text-fig. 25h ).

Pollen grains in S172560 vary markedly in size and may be immature but are also partly obscured by residual organic material. They show a gradation, from grains that are almost smooth, to grains with a very weakly developed reticulum ( Text-fig. 26b, c ). Pollen grains in specimen S172560 are also smaller than in the two other specimens, about 12 µm in diameter, and in some grains the reticulum is denser. The inner surface of the anther wall in the dehisced specimen is finely granular, probably reflecting the presence of tiny orbicules.

Affinity and other occurrences. For the possible systematic relationships of Elasmostemon paisii see comments on the genus above. The stamen fragments are closely similar to the specimen described below as “Laminar stamen with monocolpate reticulate pollen”. However, the pollen in the two stamen types differ in the details of their wall structure. Similar stamens have not been encountered in other mesofossil floras from Portugal. Melloniflora E.M.FRIIS, P.R. CRANE et K. R.PEDERSEN, and several different isolated stamens from the Early Cretaceous Puddledock flora of Virginia, USA, have pollen sacs that are embedded in the staminal tissue in a non-marginal position, but they differ in their larger size and their more elongate, scale-like form ( Friis et al. 2020b) .

Figures

Text-fig. 25. Scanning electron microscope (SEM) images of stamens and pollen grains of Elasmostemon paisii gen. et sp. nov.; Catefica locality, Portugal. a) Stamen fragment showing two pairs of pollen sacs along the margins of the stamen with a broad connective that separates the thecae, except near the apex where the thecae meet; b) Detail of surface of pollen sacs showing larger cells (arrows), interpreted as ethereal oil cells; c) Pollen in situ from specimen in (a); d) Stamen fragment with apical and basal portion missing and surface slightly abraded and compressed obscuring cellular details; note remains of another stamen attached to the underside of the stamen; e–h) Pollen in situ from specimen in (d) showing long aperture (e) and pollen wall with heterobrochate reticulum (e–h); note narrow muri with flatten and smooth surface and short columellae (h). Specimens, Catefica 49-S115859 (a–c), Catefica 151-S105281 (holotype, d–h). Scale bars = 600 Μm (a, d), 50 Μm (b), 6 Μm (c, e–g), 1.5 Μm (h).

Text-fig. 26. Scanning electron microscope (SEM) images of stamens and pollen grains of Elasmostemon paisii gen. et sp. nov. (a–c) and laminar stamens with monocolpate reticulate pollen sp. (d–g); Catefica locality, Portugal. a) Stamen fragment with basal portion missing showing two pairs of pollen sacs on one surface of the stamen close to the margin and separated by a broad connective, except near the apex where the thecae meet; note that the thecae are dehisced with the walls of the pollen sacs curled back; b) Pollen grains inside a dehisced pollen sac; note variation in size and development of the reticulum; c) Detail of (b) showing monocolpate, reticulate pollen with lumen of reticulum varying markedly in size but partly obscured by residual organic material; d) Stamen with apical and basal part of anther preserved showing two pairs of pollen sacs (asterisks) on the curved, perhaps ventral, surface close to the stamen margin; e) Detail of crack in the anther showing the inner anther wall with densely spaced spherical orbicules that vary greatly in size; f) Pollen exposed in the crack in the anther; note coarsely foveolate to coarsely reticulate pollen wall and densely spaced orbicules; g) Folded pollen grains with reticulate pollen wall and also showing the inner anther wall with densely spaced spherical orbicules that vary greatly in size. Specimens, Catefica 49-S172560 (a–c), Catefica 50- S170384 (d–g). Scale bars = 600 Μm (a, d), 20 Μm (b, e), 6 Μm (c, f, g).