Polytrichastrum incurvum HEDENÄS, BOMFLEUR et E.M. FRIIS, 2023

Bomfleur, Benjamin, Hedenäs, Lars, Friis, Else Marie, Crane, Peter R., Raunsgaard, Kaj, Pedersen, Mendes, Mário Miguel & Kvaček, Jiří, 2023, Fossil Mosses From The Early Cretaceous Catefica Mesofossil Flora, Portugal - A Window Into The Mesozoic History Of Bryophytes, Fossil Imprint 79 (2), pp. 103-125 : 105-107

Polytrichastrum incurvum HEDENÄS, BOMFLEUR et E.M. FRIIS sp. nov.

Text-figs 3a–g , 4a–d

H o l o t y p e. S174251 (Catefica sample 49; figured

Text-fig. 3a–g ).

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.

PFN003145.

P a r a t y p e s. S266391, S266392 [Catefica sample 49; figured Text-fig. 4a–d (S266392)]

R e p o s i t o r y. Palaeobotanical Collections,

Department of Palaeobiology, Swedish Museum of Natural History, Stockholm, Sweden.

E t y m o l o g y. The specific epithet refers to the incurved leaf margins.

T y p e l o c a l i t y. Catefica (39° 03ʹ 30ʺ N, 09°14ʹ 30ʺ

W), between the villages of Catefica and Mugideira, about 4 km south of Torres Vedras, Portugal.

T y p e s t r a t u m a n d a g e. Almargem Formation,

Early Cretaceous (Aptian–early Albian).

S p e c i f i c d i a g n o s i s.A species of Polytrichastrum

G.L. SM. with distinctly incurved margins of the leaf limb and upper cells of the lamellae that are thin-walled or only slightly thickened distally.

D i s t i n g u i s h i n g f e a t u r e s. Polytrichastrum incurvum differs from all extant species of Polytrichastrum in having thin-walled or only slightly distally thickened upper cells of the lamella. Among fossil taxa, P. incurvum differs from the gametophytes associated with Eopolytrichum antiquum KONOPKA, HEREND., G.L. MERR. et P.R. CRANE ,

which is of Late Cretaceous (Santonian-Campanian) age

(Konopka et al. 1997), in having widely incurved marginal laminae in the leaf limb. Meantoinea alophosioides BIPPUS ,

STOCKEY, G.W. ROTHWELL et TOMESCU, which is of Early

Cretaceous (Valanginian) age (Bippus et al. 2017), differs in having lower leaf lamellae that are 2–3 cells high (rather than 3–4(–5) cells high in P. incurvum ), also in having a distinctly mammillose adaxial lamina surface, in having finely toothed leaf margins, and in lacking the strongly curved lamina margins typical of P. incurvum .

D e s c r i p t i o n a n d C o m m e n t s o n t h e

M a t e r i a l. Three shoot fragments (S174251, S266391,

S266392) are known of which the largest is ca. 2.5 mm long.

The stem is compressed, and details are not visible except that the cortex consists of 1(–2) layers of incrassate cells which are much smaller than the cells toward the center of the stem. The leaves are erect on the stem with their distal portions incurved ( Text-figs 3a , 4a, b ). From a broad sheathing base, each leaf narrows to a limb that gradually narrows further in its upper portion to a cucullate, obtuse apex ( Text-figs 3a , 4a, b ). The costa is broad and somewhat narrower in the sheathing portion of the leaf. In the limb,

the costa has an abaxial epidermis of broader cells with thick outer walls, one layer of guide cells ca. 8–13 µm in diameter, and 3–6 layers of abaxial stereids and 0–2 layers of adaxial stereids ca. 2–4 µm in diameter. On the adaxial leaf surface the costa is covered with straight leaf lamellae.

Near the leaf apex there are 3–4 lamellae, farther down there are between 11–17(–20) lamellae ( Text-figs. 3b–e , 4c ).

The lamellae are mostly 3–4 cells high, occasionally up to 5(–6) cells high, with the upper cells thin-walled or slightly thickened. The leaf lamina is unistratose, but towards the costa can be occasionally or entirely bistratose. In the limb,

the leaf lamina is broadly incurved over the lateral lamellae

( Text-figs 3b, c , 4b ). The leaf margin is entire or slightly uneven, but not dentate or denticulate. The lamina cells of the sheathing portion of the leaf are linear, whereas they are irregularly rectangular or quadrate in the transition to the leaf limb and above.

S y s t e m a t i c R e l a t i o n s h i p s. Extant Polytrichales comprise about 19 extant genera, most of which have photosynthetic lamellae on the upper leaf surface. In gametophyte features, Polytrichastrum is similar to

Polytrichum HEDW. , from which it differs mainly in sporophytic characters (Bell and Hyvönen 2010). However, our species is referred to Polytrichastrum due to its unique similarity to Polytrichastrum sexangulare (FLÖRKE ex BRID.)

G.L. SM. and some phenotypes of what has been called ’ P.

norwegicum (HEDW.) SCHLJAKOV’ (nomenclature unclear) in regard to the incurved leaf margins. This feature is not found in Polytrichum and therefore we do not hesitate to place our fossil species in Polytrichastrum .

Polytrichastrum incurvum has leaves smaller than many extant species of Polytrichaceae , which may have shoots up to several decimetres tall and well-developed leaves of more than a centimetre long. However, the size of the leaves of P.

incurvum are well within the range seen among young leaves of the extant species. Assignments to extant genera have also been adopted in systematic treatments of other fossil bryophytes (e.g., Konopka et al. 1998, Bippus et al. 2021) For example, both Campylopodium allonense KONOPKA, HEREND.

et P.R. CRANE (Konopka et al. 1998) and Cynodontium luthii

Bippus, G.W. ROTHWELL et STOCKEY (Bippus et al. 2021) were accepted as members of extant genera in the recent overview by Ignatov and Maslova (2021).

Figures

Text-fig. 3. Scanning electron microscope (SEM, a–e) and synchrotron radiation X-ray tomographic microscopy (SRXTM, f–g) images of a shoot and leaves of Polytrichastrum incurvum HEDENÄS, BOMFLEUR et E.M.FRIIS from the Early Cretaceous Catefica mesofossil flora, Almargem Formation, Portugal. a: Shoot apex showing several incurved leaves. b: Leaf showing ventral longitudinal lamellae (arrow) and incurved leaf margins. c: Detail of longitudinal lamellae on the ventral leaf surface (arrow) and the incurved leaf margin. d: Transverse fracture through the upper portion of leaf showing lamellae on the ventral surface (arrows). e: Detail of upper surface of three longitudinal lamellae showing outlines of individual cells. f: Transverse section (orthoslice xy0655) of shoot and several leaves at different levels. Note the lamellae on the ventral surface over the costa in sections in the distal part of the leaf (arrow) and the mostly unistratose leaf lamina with smooth cells (arrowheads) and lacking lamellae in the proximal part of the leaf. g: Longitudinal section (orthoslice yz1435) showing shoot with several leaves. Specimen, Catefica 49-S174251 (a–g; holotype). Scale bars = 1 mm (a), 200 µm (b, f, g), 100 µm (c), 50 µm (d), 10 µm (e).

Text-fig. 4. Synchrotron radiation X-ray tomographic microscopy (SRXTM) images (volume renderings, a, b; orthoslices, c, d) of a shoot and leaves of Polytrichastrum incurvum HEDENÄS, BOMFLEUR et E.M.FRIIS from the Early Cretaceous Catefica mesofossil flora, Almargem Formation, Portugal. a, b: Shoot apex showing incurved leaves with distinctly incurved leaf margins. Note a section through the proximal part of a leaf (b) showing lamellae (arrow) over the costa and the unistratose leaf lamina (arrow head). c: Transverse section (orthoslice xy1440) of a shoot showing sections through the distal portions of six leaves showing the distinct lamellae (arrows). d: Transverse section (orthoslice xy2160) of a shoot showing sections through the proximal portions of several leaves showing the unistratose leaf lamina (arrow) with smooth cells. Specimen, Catefica 49-S266392 (a–d). Scale bars = 1 mm (a), 500 µm (b), 200 µm (c, d).