Trochodendron rosayi, 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 : 46-48

Trochodendron rosayi sp. nov.

Text-fig. 2 a–d

H o l o t y p e. UF 18110-70162 ( Text-fig. 2b, c ), designated here.

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.

PFN000100 (for new species).

E t y m o l o g y. This species is named in honor of Robert Rosé (pronounced “Rosay”) who collected and donated the specimens.

T y p e l o c a l i t y. Moose Mountain near Cascadia Oregon ( UF locality 18110, 44° 26.5790′ N, 122° 18.9570′ W) , USA.

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

Series, middle Miocene.

A d d i t i o n a l o c c u r r e n c e. Emerald Creek, Idaho ( Trochodendron sp. in Manchester et al. 1991), Sucker Creek, Oregon ( Fields 1996a: pl. 3, figs 1, 3).

D i a g n o s i s. Fruits turbinate to subglobose capsules, broadly rounded apically, tapered basally, with about 10 persistent styles arising about 2/3 of the distance from base to apex. Styles straight to curving outward (convexly). Pedicels slender, ca. twice as long as the fruit length. Capsule surface mostly smooth, opening apically with radiating loculicidal slits, a slit arising above each style and joining with other slits to form a large, polygonal aperture at fruit apex when dehiscing. Nectaries flattened, triangular, extending from the equatorial region of the fruit to the base of each style. Stamen scars numerous (ca. 25 in total) scattered in a broad band at the junction between pedicel and expanded part of the fruit body.

D i m e n s i o n s. Fruits 5.7 mm wide, 7.5–10 mm high, Styles 1.8–2.3 mm long, Nectary below each style ca. 1.5 mm wide, 2.0 mm high. Pedicels 1.0 to 1.2 mm thick and at least 18–20 mm long. Infructescence axis 1.8 to 2.0 mm thick.

R e m a r k s. We consider the rare specimens previously illustrated from Emerald Creek, Idaho ( Text-fig. 2d ; Manchester et al. 1991) and Sucker Creek, Oregon ( Fields 1996a, b) to be conspecific with the type material from the Moose Mountain flora. Triangular flattened areas beneath each of the styles ( Text-fig. 2c ) are shaped and positioned like the nectaries in the extant species ( Text-fig. 2f, g ). Elliptical verrucae near the base of the fruit, imaged by x-ray tomography of the holotype ( Text-fig. 2c ), appear to represent the scars of numerous shed stamens and are positioned as in extant fruits ( Text-fig. 2f ).

Trochodendron rosayi fruits are very similar to those of extant T. aralioides SIEBOLD et ZUCCARINI ( Text-fig. 2 e–g), and apparently to the Miocene species Trochodendron kamtschaticum CHELEBAEVA et CHIGAEVA from Kamchatka and to the infructescence associated with leaves of T. protoaralioides MURAI ( Uemura 1988) from the late Miocene of Japan ( Manchester et al. 1991: figs 30, 33). These Asian Miocene specimens have a similar size, shape and number of carpels but the persistent stamen scars were not confirmed.

It is instructive to compare T. rosayi with Trochodendron infructescences known from older strata of the Okanogan Highlands Eocene. Two infructescences from Republic described as Trochodendron sp. ( Pigg et al. 2001) have pedicellate fruits of similar morphology, but the fruits are much smaller: 1.85–2.5 mm long and 2.0– 3.7 mm wide. One isolated fruit figured in the same article, might represent a different taxon ( Pigg et al. 2001: fig. 4H; K. Pigg, personal observation). The paniculate infructesence named T. drachukii PIGG, DILLHOFF, DEVORE et WEHR from McAbee ( Pigg et al. 2007) bears fruits that are 3–4 mm long and wide and have 8 or more persistent styles. It has been difficult to determine whether those geologically older fruits bore nectaries beneath each style and whether there were staminal scars over the basal 1/3 of the fruits as in the modern species and in T. rosayi . Trochodendron rosayi thus differs from the Eocene fruits by the larger size, the direction of style curvature (straight to outward rather than inward) and the confirmed presence of stamen scars on the base of the fruits.

Figures

Text-fig. 2. Miocene and extant Trochodendron fruits. a–d) Trochodendron rosayi sp. nov. infructescences. a–c) Specimens from Moose Mountain flora, Oregon. a) Raceme bearing at least 4 fruits showing long pedicels, and outwardly protruding persistent styles, UF 18110-70164. b) Raceme showing two attached fruits and pedicels indicating at least 4 fruits, holotype, UF 18110-70162. c) Surface of one fruit of the holotype (UF 18110-70162), viewed through the sediment from behind from CT scan data. Arrows indicate 4 of the styles (more can be inferred from symmetry) each with a nectary beneath. d) Infructescence from Emerald Creek, Idaho; composite image assembled from images both incomplete counterpart specimens, reflected light, UF 18630-9575. e) Racemose infructescence of extant Trochodendron aralioides, reflected light. f, g) Individual fruits from (e), enlarged, isosurface images from CT scan data. Fruits with ten and six styles; note staminal scars seen in (f). Scale bars calibrated in mm.