Dictyozonia pusilla E.M.FRIIS, P.R.CRANE et K.R.PEDERSEN, 2019

Friis, Else Marie, Crane, Peter R. & Pedersen, Kaj Raunsgaard, 2019, The Early Cretaceous Mesofossil Flora Of Torres Vedras (Ne Of Forte Da Forca), Portugal: A Palaeofloristic Analysis Of An Early Angiosperm Community, Fossil Imprint 75 (2), pp. 153-257 : 221-223

Dictyozonia pusilla E.M.FRIIS, P.R.CRANE et K.R.PEDERSEN sp. nov.

Text-fig. 44f–k

H o l o t y p e. Designated here. S105002 (Torres Vedras sample 144; figured Text-fig. 44f–k ).

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.

PFN000523 (for new species).

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

E t y m o l o g y. From Latin: pusillus, very small, referring to the very small size of the pollen grains.

T y p e l o c a l i t y. Torres Vedras (NE of Forte de

Forca; 39°06′13″ N, 9°14′47″ W).

T y p e s t r a t u m a n d a g e. Lower member of the Almargem Formation; Early Cretaceous (late Barremianearly Aptian).

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

D i m e n s i o n s. Diameter of pollen grains: about

9–12 µm.

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 a fragment of a tetrasporangiate stamen ( Text-fig. 44f ) with pollen in situ ( Text-fig. 44g –k ). The pollen grains were briefly described and illustrated earlier as pollen type “B.4 monocolpate, psilate-reticulate pollen” ( Friis et al. 1999), but the material was not formally named. The pollen grains are small, almost circular in equatorial outline, and monocolpate. The pollen wall is semitectate-reticulate in the equatorial region, and psilate to psilate-punctate in the polar regions ( Text-fig. 44g –k ). The reticulum forms a distinct band around the equator ( Text-fig. 44g, k ). The reticulum is heterobrochate with a narrow microreticulate to foveolate zone bordering the psilate regions of the distal and proximal poles. In the polar regions the tectum is psilate with a narrow punctate zone close to the colpus margin ( Text-fig. 44j ). Muri are smooth with slightly rounded profile, and are supported by short, scattered columellae. The colpus extends for the full length of the grains and has a distinct margin and verrucate membrane ( Text-fig. 44h–j ).

A f f i n i t y a n d o t h e r o c c u r r e n c e s. Dictyozonia pusilla is only known from the Torres Vedras mesofossil flora. A probably related pollen type with psilate polar regions and a semitectate equatorial region was observed in a small flower fragment from the Buarcos mesofossil flora (Pollen Type B. 3 in Friis et al. 1999). However, in the Buarcos specimen both monocolpate and trichotomocolpate pollen occur in the same anther and the tectum in the equatorial region is microreticulate to foveolate. Pollen grains with extended psilate polar regions and reticulate equatorial regions have been described from the Early Cretaceous of the Potomac Group by Walker and Walker (1986) who suggested an affinity for these grains with extant monocots, but so far we have been unable to place Dictyozonia pusilla in any modern taxon.

Very small pollen grains somewhat comparable to those of Dictyozonia pusilla with a graded reticulum and foveolate to psilate proximal face were also described from the Albian of Egypt as Reticoll-Smallpatch and Crochetret- Baldap ( Penny 1991), but none of these has a similar narrow reticulate equatorial band and psilate areas on the distal face.

Figures

Text-fig. 44. Scanning electron microscope (SEM) images of monocolpate pollen of Juhaszia portugallica gen. et sp. nov. from a fragment of a pollen sac (a–e) and stamen fragment and pollen of Dictyozonia pusilla gen. et sp. nov. (f–k); Torres Vedras locality, Portugal. a) Holotype; fragment of pollen sac that yielded the pollen in (b–e); b) Proximal surface of pollen grain showing reticulate sculpture in the equatorial regions grading into more a continuous foveolate tectum at the proximal pole; c) Reticulum on the proximal surface showing smooth muri delimiting large and small luminae. Muri supported by numerous short columellae that are only loosely attached to the smooth surface of the foot layer; d) Distal surface of pollen grain showing the long colpus and reticulate sculpture with a distinctive pattern of large and small luminae; e) Pollen grain from which the reticulum has become