Concavistylon kvacekii, Manchester & Pigg & Devore, 2018

Manchester, Steven R., Pigg, Kathleen B. & Devore, Melanie L., 2018, Trochodendraceous Fruits And Foliage In The Miocene Of Western North America, Fossil Imprint 74 (1 - 2), pp. 45-54 : 48-49

Concavistylon kvacekii sp. nov.

Text-fig. 3 a–k

H o l o t y p e. UCMP 151875 ( Text-fig. 3a ).

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.

PFN000102 (for new species).

E t y m o l o g y. This species is named in honor of our friend, Zlatko Kvaček, recognizing his many contributions to paleobotany as well as his participation in the investigation of other fossil Trochodendraceae from western North America.

T y p e l o c a l i t y. Moose Mountain flora near

Cascadia, Oregon, USA.

T y p e h o r i z o n a n d a g e. Little Butte Volcanic

Series, middle Miocene.

D i a g n o s i s. Infructescence axis relatively stout, pedicels very short, or fruits subsessile. Capsules 4 to 6 carpellate; styles persistent, concave toward the fruit apex.

D i m e n s i o n s. Raceme 1.3–1.8 mm wide. Infructescence 40–51 mm long; capsules 3–4 mm high, 2.5–3.4 mm wide; styles 1.5–2 mm long, concave toward the fruit apex.

R e m a r k s. Concavistylon is a new genus of infructescence with a combination of characters found separately in the two extant genera of Trochodendraceae , along with some unique features. The fruits are shortly pedicellate or subsessile, resembling Tetracentron which has sessile fruits. Unlike Tetracentron , which has four basal tepals that persist even to fruiting stage, these fruits appear to lack perianth, and in this respect resemble Trochodendron . The number of styles is small (4–5; Text-fig. 3 f–k) as in Tetracentron (4) rather than more abundant (7–9 in Trochodendron ). The dehiscence is apical by convergent loculicidal slits as in both extant genera. The distal displacement of the styles toward the edge of the gynoecium coincides with the development observed in both modern genera ( Endress 1986). However, the styles are curved inward toward the apex of the fruit, rather than turned outward as in Miocene and extant Tetracentron and Trochodendron species.

Infructescences that appear to represent Concavistylon are also known from the Eocene of Republic, Washington and McAbee, British Colombia but in those occurrences the pedicels are longer whereas the fruits of the Moose Mountain species are subsessile. One such specimen was previously identified as the extant genus ( Manchester et al. 2009), but has been confirmed by CT scan to have fewer carpels (5–6) than modern Trochodendron . One specimen from Republic ( Manchester et al. 2017) is particularly informative because it bears both fruits and foliage on the same twig, proving that a pinnately veined leaf type similar to that of modern T. aralioides was borne by the same plant as Concavistylon . Such leaves also occur at McAbee where several Concavistylon infructescences have been recovered. We expected that similar leaves might be common in the Miocene of Moose Mountain, but only one such leaf is known in the collections, and its preservation is not good enough to be sure of its identity.

Figures

Text-fig. 3. Concavistylon kvacekii gen. et sp. nov. from Moose Mountain flora, Oregon. a) Infructescence reflected light, holotype, UCMP 151875. b) Digital profile of the same infructescence, CT scan data, viewed through the sediment (rendered transparent) from behind. c) Raceme with several fruits showing styles concave toward fruit apex, UCMP 201233. d) Raceme with stout axis, UCMP 201232. e) Long slender specimen, with fruits spaced farther apart, possibly immature, UCMP 201231. f) Detail from (c), showing persistent styles, light microscopy. g) Detail from (b), CT scan surface rendering. Note 5 styles arising from upper left fruit. h) Infructescence with at least 18 fruits, reflected light, UF 18110-70163. i) Same specimen as (a), (b), (g), imaged with depth map rendering, showing apically opening capsules and 5 apically directed styles on each fruit, (j) same as (h), isosurface from CT scan data, showing apical opening of capsules. k) Depth map rendering of the specimen in (h), (j). Scale bars = 1 cm in (a–e), (h–j); 5 mm in (f), (g).