Gastonispermum portugallicum, Friis & Crane & Pedersen, 2018

Friis, Else Marie, Crane, Peter R. & Pedersen, Kaj Raunsgaard, 2018, Extinct Taxa Of Exotestal Seeds Close To Austrobaileyales And Nymphaeales From The Early Cretaceous Of Portugal, Fossil Imprint 74 (1 - 2), pp. 135-158 : 138-140

Gastonispermum portugallicum gen. et sp. nov.

Text-figs 1–2

H o l o t y p e. Designated here, S174820 (Famalicão sample 025; illustrated here in Text-figs 1d–f , 2a, d).

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.

PFN000089 (for new species).

P a r a t y p e s. Designated here, S105218, S105220, S170234, S174343, S174430, S174435, S174819, S174821, S175044, S175045, S175082, S175084, S175095, S175100 – S175104 (Famalicão sample 025).

R e p o s i t o r y. Palaeobotanical Collections, Department of Palaeobiology, the Swedish Museum of Natural History, Stockholm, Sweden (S).

E t y m o l o g y. The species is named for Portugal where the fossils were collected.

T y p e l o c a l i t y. Famalicão , Portugal (39°42′16″N;

8°46′12″W).

T y p e s t r a t u m a n d a g e. Below the Figueira da Foz Formation; Early Cretaceous (late Aptian – early Albian or older).

D i a g n o s i s. As for the genus.

D i m e n s i o n s. Length of seeds: 1.2–1.7 mm; width of seeds: 0.8–1.3 mm.

O t h e r s p e c i m e n s. S175108 (Vale de Água sample

330); S175110 (Vale de Água sample 333).

D e s c r i p t i o n a n d r e m a r k s. The species is based on about 230 isolated seeds of which 14 specimens were studied using SRXTM ( S105218 , S105220 , S170234 , S174343 , S174430 , S174435 , S174819 , S174820 , S174821 , S175044 , S175045 , S175082 , S175084 , S175095 ). There is no information on the fruits in which the seeds were borne. The seeds are small, anatropous, bitegmic and exotestal with bilateral symmetry. They are elliptical in lateral view ( Text-figs 1a–e, h , 2a) and also in transverse section (Textfig. 2g). The seed surface is dull, almost smooth, but with a jigsaw puzzle-shaped pattern formed from the slightly raised undulate anticlinal walls of the exotesta cells .

Micropyle and hilum are very close together and displaced towards the raphal side of the seed ( Text-fig. 1a– d ). The hilum is small, circular in outline and slightly raised without a hilar rim ( Text-fig. 1g ). The course of the raphe is distinct on the seed surface and seen as a slightly raised, rounded ridge that extends from hilum to the chalazal end of the seed ( Text-fig. 1a, b ). The micropyle is formed from the inner integument. The position of the micropyle is marked by a branched, Y-shaped slit in the testa ( Text-figs 1g , 2b). Internally the micropylar slit is lined by testal cells on all sides ( Text-fig. 2a, b).

The seed coat is composed of a thick exotesta, a thinner mesotesta/endotesta, and a thin tegmen. The exotesta consists of a single layer of tall, columnar sclerenchyma that vary in height from about 55 µm laterally and on the antiraphal sides of the seed, to about 80 µm over the raphe ( Text-figs 1e, h , 2a, g). In the micropylar region the columnar sclerenchyma cells are shorter and become much shorter towards the micropylar slit ( Text-figs 1e, f, h , 2a, c, e). The exotestal cells are arranged in indistinct longitudinal rows. The anticlinal walls of the exotestal cells are thickened, slightly raised on the surface, and of almost even thickness from the outside to the inside, resulting in an almost straight lumen ( Text-figs 1h , 2a, g). Towards the outside and inside they are strongly undulate resulting in stellate-undulate facets and a jigsaw puzzle-like pattern on the surface with rounded, undivided lobes ( Text-fig. 1i ). Exotestal cells are also undulate over the raphe. Exotesta cells around the micropylar slit are slender and tall ( Text-fig. 2c). The mesotesta/endotesta consists of two or three layers of collapsed parenchyma cells with thick cell walls ( Text-fig. 2a). The tegmen is thin and composed of cells that are collapsed over most of the seed, but more robust and slightly thickened in the micropylar region.

Nutritive tissue is partly preserved in five of the specimens that were studied using SRXTM. Two of these specimens (S174820, S174821) also had a complete embryo preserved. In both cases the embryo is tiny, about 130 µm long and 130 µm broad, with two rudimentary cotyledons and an embryo to seed (E: S) ratio of about 0.02. The embryo is composed of cells that are much smaller than the surrounding nutritive tissue. Each cell contains a dense, central structure that may be the fossilized remains of a nucleus ( Text-figs 1e, f , 2a, d, e). The nutritive tissue is cellular, consisting of isodiametric and thin-walled cells, about 40 µm in diameter ( Text-fig. 2a, e, f). Cell walls are slightly undulating or straight. In some specimens the cells of the nutritive tissue are empty ( Text-fig. 2f), but in other cases these cells are filled by small granules. These granules are often clustered close to the cell walls ( Text-fig. 2e) and we interpret them to be the remains of protein or lipid bodies. We interpret the nutritive tissue immediately surrounding the embryo as endosperm (Textfig. 2e), but the continuity of this inner tissue with the bulk of the nutritive tissue in the outer parts of the seed is not clear, and thus the possibility that the outer tissues may be perisperm cannot be definitively excluded.

Figures

Text-fig. 1. Gastonispermum portugallicum gen. et sp. nov. seeds from the Early Cretaceous Famalicão locality (sample 025), Portugal; Synchrotron radiation X-ray tomographic microscopy (SRXTM, volume renderings). Note remains of mounting media on several seeds (¤). a) Seed in oblique view showing seed shape, the slightly raised raphal ridge and the position of hilum (hi) and micropyle (mi) on the raphal side of the seed (S170218). b, c) Seeds in lateral view (b, S170234; c, S175095). d–f) Holotype (S174820); seed in lateral view (d) and cut volume rendering (e, f) through the median plane of the seed showing palisade-shaped sclerenchyma cells of exotesta and remains of embryo (emb) and surrounding nutritive tissue (e, cut between yz0440-0530; f, cut between slices yz440-480). g) Hilum (hi) and micropyle (mi) of seed in (1a) showing the Y-shaped micropylar slit in the outer integument. h) Cut volume rendering through the median plane of the seed (cut at yz0492) showing seed coat mainly composed of palisade-shaped cells of the exotesta (S174435). i) Seed surface showing the raised outlines of the undulate anticlinal walls of the exotestal cells (S175045). Scale bars = 500 µm (a–e); 250 µm (g); 125 µm (f, i).