Pennipollis sp.

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 : 205-206

Pennipollis sp.

Text-fig. 35b–d

D e s c r i p t i o n a n d r e m a r k s. Pollen grains of Pennipollis sp. occur in a pollen clump that is probably a stamen fragment ( Text-fig. 35b ), and also in a coprolite together with several different kinds of pollen grains. Pollen grains are spherical, about 18 µm in diameter and monocolpate. The exine is semitectate-reticulate and acolumellate, with scattered supratectal spinules. The spinules have pointed tips and are arranged in one or two rows along the margin of the muri ( Text-fig. 35c, d ). Lumina are of various sizes, but are generally large and up to about 3 µm long.

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. The pollen grains of Pennipollis sp. from Torres Vedras are closely similar to grains found in situ in isolated stamens and in a fragment of a staminate inflorescence of Pennistemon portugallicus E.M.FRIIS, K.R.PEDERSEN et P.R.CRANE described from the Vale de Água mesofossil flora ( Friis et al. 2000b). However, the grains of Pennistemon portugallicus are smaller, the lumina are generally larger and the supratectal elements are blunt and more densely distributed. In supratectal ornamentation the grains from Torres Vedras are more similar to grains of Pennipollis peroreticulatus (G. J.BRENNER) E.M.FRIIS, K.R.PEDERSEN et P.R.CRANE described from the Albian of Oklahoma by Walker and Walker (1984) as Retimonocolpites peroreticulatus (G.J.BRENNER) J.A.DOYLE. Whether these grains are similar to the holotype from the Potomac Group sediments is uncertain as Brenner’s original material was studied only using LM.

Fossil remains of the Pennistemon plant (Pennistemon E.M.FRIIS, K.R.PEDERSEN et P.R.CRANE, Pennicarpus and Pennipollis ) are relatively well known, and although rare at the Torres Vedras locality, are common in the Vale de Água and Buarcos mesofossil floras ( Friis et al. 2000b). In the Torres Vedras mesofossil assemblage remains of the Pennistemon plant include only three fruits of Pennicarpus and pollen grains of Pennipollis from two pollen clumps and a coprolite. Pollen of Pennipollis is also reported from coastal sections in Portugal ( Heimhofer et al. 2007) ranging from the early Aptian to the middle Albian.

Based on the more abundant and better preserved specimens from the Vale de Água locality we suggested an affinity of the Pennistemon plant to monocotyledons, and particularly to Araceae , although the fossils could not be assigned to any existing taxon ( Friis et al. 2000b). Based on pollen alone Doyle and Hotton (1991) suggested affinity with Chloranthaceae , and a chloranthaceous affinity has been repeatedly advanced based on phylogenetic analyses that have also included features from the fossil fruits and stamens (e.g. Doyle and Endress 2014). However, the pollen grains of Pennipollis are fundamentally different from the pollen of all extant and securely analyzed extinct chloranthoid taxa in the absence of columellae and the presence of a fine granular infratectal layer. In the pollen of all unequivocal Chloranthaceae there is no granular infratectal layer and the tectum is supported by well-developed columellae. In addition, in the pollen grains of all Chloranthaceae that have a supratectal ornamentation, the sculptural elements are densely arranged and composed of minute, rounded elements, whereas in Pennipollis the sculpturing elements are spiny with acute tips and typically much less densely distributed. Sculpturing elements of this kind are not reported for Chloranthaceae , but closely similar supratectal ornamentation is known for pollen of some extant Alismatales and other monocotyledons, a group that has been poorly represented in the phylogenetic analyses performed to date. For example, pollen of Aponogeton L.f. is monocolpate and sometimes with very short columellae ( Grímsson et al. 2014). Similarly, acolumellate pollen is characteristic of several other taxa among Alismatales ( Grayum 1992) . All fossil fruits and stamens associated with Pennipollis are compressed and preserve few distinctive features. More informative material will be needed for a secure assessment of the phylogenetic position of the Pennistemon plant among monocotyledons and other early diverging angiosperm groups.

Figures

Text-fig. 35. Scanning electron microscope (SEM) images of a fruit of Pennicarpus sp. and monocolpate pollen of Pennipollis sp. from a pollen clump;Torres Vedraslocality, Portugal. a) Fruit of Pennicarpus sp. showing the poorly preservedfruit wall enclosing a single seed; b) Pollen clump that yielded the pollen in thisText-figure (c, d); c, d) Pollen grains showing the loose reticulum bearing smallspinules that are often in two rows; note the smooth surface of the foot layer, the absence of columellae, the continuous muri bordering the apertures and spiny orbicules (arrowheads). Specimens, TV38-S174609 (a), TV44-S148015 (b–d). Scale bars 300 Μm (a, b), 6 Μm (c, d).