Appomattoxia minuta E.M.FRIIS, K.R.PEDERSEN et P.R.CRANE, 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 : 190-193

Appomattoxia minuta E.M.FRIIS, K.R.PEDERSEN et P.R.CRANE sp. nov.

Text-fig. 25a–g

H o l o t y p e. Designated here. S136786 (Torres Vedras sample 44; figured Text-fig. 25a, d, e ).

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.

PFN000458 (for new species).

P a r a t y p e s. Designated here. S105022 (Torres Vedras sample 43); S136787, S136788, S148010 (Torres Vedras sample 44).

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: minutus referring to the small size of the fruits.

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).

S p e c i f i c d i a g n o s i s. As for the genus with the following additions: Fruits minute, narrowly elliptical to ovate in outline, borne on a short oblique stalk. Outer epidermal cells of fruit wall large, each bearing a central long and narrow trichome that is only slightly recurved at the tip. Stigma sessile, indistinct without trichomes. Pollen grains circular to elliptical in outline, monocolpate with short colpus. Exine tectate, irregularly verrucate and microechinate.

D i s t i n g u i s h i n g f e a t u r e s. Fruits of Appomattoxia minuta differ from those of the type species, A. ancistrophora E.M.FRIIS, K.R.PEDERSEN et P.R.CRANE described from the Early Cretaceous Puddledock mesofossil flora of Virginia, USA ( Friis et al. 1995), mainly in their much smaller size (fruits 0.45–0.75 mm long and 0.3– 0.4 mm wide compared to 0.6–2.0 mm long and 0.5–1.5 mm wide in A. ancistrophora ). The trichomes on the fruit surface are also narrower and less robust than in A. ancistrophora . Further, the tips of the spines are only slightly recurved in A. minuta , but distinctly hook-shaped in A. ancistrophora . Pollen grains are closely similar to those of A. ancistrophora , but the colpus is shorter.

D i m e n s i o n s. Length of fruits: 0.45–0.75 mm; width of fruits: 0.3–0.4 mm. Length of spines: 0.15 mm. Diameter of pollen grains: about 16 µm.

D e s c r i p t i o n a n d r e m a r k s. Appomattoxia minuta is based on five isolated fruits. There is no information on how the fruits were attached to the plant. Each fruit is minute, elliptical to ovate in outline. All specimens are much compressed ( Text-fig. 25a–c ). In their general organization and shape the fruits are similar to Appomattoxia ancistrophora , and are also similar in having the thin fruit wall covered by densely arranged trichomes ( Text-fig. 25a–c ). The stigmatic area is indistinct, sessile and lacks trichomes. As in A. ancistrophora , the trichomes of the fruit wall are apparently unicellular, but they are only slightly recurved at the tips and the cuticle is thin. None of the specimens were macerated or studied using SRXTM.

Many pollen grains, all of the same kind, occur entangled in the trichomes on the surface of all the fruits ( Text-fig. 25d–g ). The pollen is circular to elliptic in equatorial outline, about 16 µm in diameter and monocolpate. The colpus is short, about 6 µm long and does not reach the equator. The grains are tectate with an irregular rugulate surface covered by closely spaced and solitary microechinae ( Text-fig. 25d–g ). The colpus membrane is covered by small verrucae ( Text-fig. 25f, g ).

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 associated with Appomattoxia minuta are closely similar to those occurring in situ in dithecate and tetrasporangiate anthers that are assigned to Goczania rugosa . Appomattoxia minuta and Goczania rugosa may belong to the same natural species (see below).

Pollen grains found in situ in staminate flowers of Pseudoasterophyllites cretaceus FEISTM. ex VELEN. from the Cenomanian of the Czech Republic show some similarities to pollen grains associated with Appomattoxia , but differ in having a much shorter and broader colpus. Further, pollen grains of Pseudoasterophyllites cretaceus have a tectum with a mixed columellate and granular infratectal layer ( Kvaček et al. 2016) in contrast to the granular infratectal layer documented by TEM for Appomattoxia ancistrophora from the Puddledock mesofossil flora ( Friis et al. 1995). Fruits of Pseudoasterophyllites cretaceus also differ from those of Appomattoxia in several respects, including the lack of trichomes and the presence of stomata on the fruit wall, and in having a short decurrent stigma ( Kvaček et al. 2016).

A piperalean affinity was suggested for Appomattoxia by Friis et al. (1995), based on combined features of the fruits, seeds and pollen. Monocolpate, tectate and microechinate grains that are especially similarity to grains of Appomattoxia are known in extant Piper L.( Grayum 1992).Extant Peperomia RUIZ et PAV. has inaperturate pollen, but also has pollen grains resembling those associated with A. ancistrophora and A. minuta in their supratectal ornamentation and rugose pollen wall (e.g. Halbritter and Buchner 2016).

Doyle and Endress (2014) suggested a relationship to Chloranthaceae rather than Piperales for Appomattoxia , and emphasized the presence of supratectal microechinate (spinules) on the tectum as a feature shared between the pollen associated with Appomattoxia and pollen of Chloranthaceae . However, supratectal microechinae occur in many different angiosperms and a fully tectate pollen wall is not known for any extant or fossil chloranthoid taxon. All extant and fossil chloranthoids have a semitectate-reticulate pollen wall, while all extant Piperales are characterized by tectate pollen. Securely resolving the putative chloranthoid versus piperalean affinities of Appomattoxia will require additional information on the parent plants that produced these fruits, but the difficulties of assigning these fossils to an extant group are illustrative of the broader problem of determining the relationships of Early Cretaceous fossils in the face of massive extinction in the early phases of angiosperm diversification ( Friis et al. 2019a).

Figures

Text-fig. 25. Scanning electron microscope (SEM) images of Appomattoxia minuta sp. nov. fruits and associated monocolpate pollen grains; Torres Vedras locality, Portugal. a–c) Lateral view of fruits (a, holotype) covered with hooked hairs showing the apical stigmatic area; d–g) Pollen grains from the fruits in (a) and (b) showing short monocolpate aperture, granular aperture membrane and microechinate tectum. Specimens, TV44-S136786 (holotype; a, d, e), TV44-S136787 (b, f, g), TV43-S105022 (c). Scale bars 300 Μm (a–c), 30 Μm (e), 6 Μm (d, f, g).