Rightcania kvacekii E.M.FRIIS, P.R.CRANE et K.R.PEDERSEN
Friis, Else Marie, Crane, Peter R. & Pedersen, Kaj Raunsgaard, 2018, Rightcania And Kvacekispermum: Early Cretaceous Seeds From Eastern North America And Portugal Provide Further Evidence Of The Early Chloranthoid Diversification, Fossil Imprint 74 (1 - 2), pp. 65-76: 69-71
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|Rightcania kvacekii E.M.FRIIS, P.R.CRANE et K.R.PEDERSEN|
Text-figs 1–2 View Text-fig
H o l o t y p e. Designated here, PP56562 (Puddledock sample 185; illustrated here on Text-figs 1a–e View Text-fig , 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.
PFN000105 (for new species).
P a r a t y p e s d e s i g n a t e d h e r e. PP56566 – PP56568 (Puddledock sample 183); PP56564, PP56565 (Puddledock sample 185); PP56593, PP56599 (Puddledock sample 189).
R e p o s i t o r y. Palaeobotanical Collections, Department of Geology, The Field Museum, Chicago, Illinois, USA (PP).
E t y m o l o g y. The name kvacekii is in honor of Zlatko
Kvaček for his contribution to palaeobotany.
T y p e l o c a l i t y. Puddledock locality, former Tarmac Lone Star Industries (Vulcan Materials Co.) sand and gravel pit, located south of Richmond and east of the Appomattox River in Prince George County, Virginia, USA (37° 15′ 52″ N, 77° 22′ 10″ W) GoogleMaps .
T y p e s t r a t u m a n d a g e. Basal part of Subzone IIB, Potomac Group; Early Cretaceous (early to middle Albian).
D i a g n o s i s. As for the genus.
D i s t i n g u i s h i n g f e a t u r e s f o r R i g h t c a n i a
k v a c e k i i. As for the genus.
D i m e n s i o n s. Length of fruit: 1.6–2.9 mm; width of fruit: 1.1–2.18 mm.
D e s c r i p t i o n a n d r e m a r k s. Rightcania is based on about 40 dispersed fruits and seed fragments, all preserved as lignite. The fruits are mostly three- or fourseeded, rarely five-seeded. The fruits are abraded, and one four-seeded fruit has remains of a hypanthium fused to the fruit wall. There is no other information on the attachment or organization of the flower.
The fruits are obovate in lateral view, almost circular in transverse section ( Text-fig. 1a–d View Text-fig ), about 1.6–2.9 mm long and 1.1–2.18 mm in diameter, with three to five ovules/ seeds. The fruit wall is preserved near the fruit apex and also in small, scattered regions over the seed surface, but it is generally abraded ( Text-fig. 2a, c–e). It is composed of thin-walled, more or less isodiametric, parenchyma cells. Cavities that may indicate the former presence of ethereal oil cells are occasionally present in the ground tissue of the fruit wall, but unequivocal resin bodies that would provide more definitive evidence have not been observed.
Well-preserved internal details revealed by synchrotron radiation X-ray microtomographic microscopy ( SRXMT) of a larger, four-seeded specimen (Holotype, PP 56562), show that this fruit was mature or close to maturity with two fully developed seeds and two underdeveloped or aborted ovules/seeds ( Text-figs 1c–e View Text-fig , 2a). The fruit is unilocular and the seeds are radially arranged, perhaps indicating that the gynoecium is syncarpous and evolved from three to five carpels each with a single seed .
The ovules/seeds are attached apically ( Text-fig. 2f) and are slightly shorter than the fruit. The ovules/seeds are elliptical to obconical in lateral view; rounded at the chalazal end (apical) and slightly pointed at the micropylar end (basal). The seeds are triangular to almost circular in transverse section with flattened or concave contact faces ( Text-fig. 1a, c, d View Text-fig ). The stigma is poorly preserved, but was apparently sessile.
The ovules/seeds are orthotropous to hemi-orthotropous, bitegmic and endotestal. The outer integument is composed of an exotesta and endotesta. The exotesta is composed of elongated sclerenchyma cells, several cell layers deep arranged longitudinally in an irregularly wavy pattern ( Text-figs 1b View Text-fig , 2b). The separation between the exotesta of adjacent seeds is often not distinct, which can give the fruit the appearance of being septate. However, the separation is clear close to the fruit wall ( Text-fig. 2e). The exotesta is up to 120 µm thick adjacent to the carpel wall and 70 µm thick between the seeds.
The endotesta has a smooth outer surface and is composed of cubic to palisade-shaped crystal cells, one cell layer deep. The cells have densely packed crystals internally that are seen as cubic imprints in the cell lumen, which is otherwise filled by an endoreticulate infilling of fibres (Textfigs 1c–e, 2a, c). The endotesta is about 60 µm thick adjacent to the carpel wall and about 30 µm thick along the contact faces between the seeds.
In the holotype analysed using SRXTM the cells of the tegmen are mostly crushed in the fully developed seeds ( Text-figs 1c–e View Text-fig , 2a), whereas in the two ovules/seeds that are thought to be underdeveloped or aborted ( Text-figs 1c, d View Text-fig , 2a), the tegmen is better preserved. In the fully developed, and also in the underdeveloped or aborted ovules/seeds the exotegmen consists of narrow, thick-walled cells. Meso- and endotegmen are only well preserved in the aborted or undeveloped ovules/seeds, where they consist of several layers of larger, thin-walled cells. The tegmen probably served as a nutritive tissue for the developing embryo and was consumed in the two fully mature seeds .
A tiny embryo is partly preserved in one of the fully developed seeds ( Text-figs 1c, e View Text-fig , 2a). It is positioned close to the micropyle and is formed of minute, almost isodiametric cells. The embryo is surrounded by larger, thin-walled cells that comprise the remains of the nutritive tissue and are interpreted as cells of the endosperm ( Text-fig. 2a).
Tavera, Department of Geology and Geophysics
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