Trochodendroides genetrix (NEWBERRY) Manchester, 2014

Manchester, Steven R., 2014, Revisions To Roland Brown’S North American Paleocene Flora, Acta Musei Nationalis Pragae Series B 70 (3 - 4), pp. 153-210 : 167-169

Trochodendroides genetrix (NEWBERRY) comb. nov.

Text-figs 7.1–7.3

1868 Populus genetrix NEWBERRY, Lyceum Nat. Hist. New York Ann., 9, p. 64; 1898 U. S. Geol. Surv. Monogr., 35, p. 44, pl. 27. fig. 1 [Basionym].

1939a Cercidiphyllum arcticum (HEER) BROWN p. 492– 494, pl. 53, figs 1, 6, Pl. 54, figs 1–3, 7; Pl. 56, fig. 1.

1962 Cercidiphyllum arcticum (HEER) BROWN p. 70, pl. 38, figs 1, 8, 14, 16.

1977 Cercidiphyllum genetrix (NEWBERRY) HICKEY p. 124, pl. 22, figs 1, 2, 4–7; pl. 23, fig. 2, pl. 24 fig. 1.

A recently recovered twig with attached leaves ( Text-fig. 7.1 ) shows the great variation of leaf from elliptical to ovate to obovate, and fan-shaped forms, and serration ranging from fine to coarse, proving that they indeed represent one species. This leads to the conclusion that the leaves called Cercidiphyllum genetrix (NEWBERRY) HICKEY , Trochodendroides serrulata (WARD) J. WOLFE (See Hickey 1977 for review) and many of those formerly treated by Brown as Cercidiphyllum arcticum (syn. Trochodendroides arctica ) represent variation in a single species. Because these leaves do not match the lectotype of T. arctica from Greenland, it seems prudent to recognize this widespread and common type of foliage from the North American Paleocene under the new combination Trochodendroides genetrix . The generic name, Trochodendroides BERRY , is based on a similar, but finely serrate, leaf from the Cretaceous Dakota Formation of Nebraska.

Archeampelos acerifolia (NEWBERRY) MCLVER et BASINGER

Text-fig. 8

1868 Populus acerifolia Newberry , p. 65; 1898, p. 37, pl. 28, figs 5–8 (Basionym)

1962 Ampelopsis acerifolia (Newberry) Brown, 1962 , [part], p. 78, pl. 51, figs 1, 3, 4, 8, 13, 16, 17.

1993 Archeampelos acerifolia (Newberry) McIver and Basinger, 1993, p. 47 (but not their figured specimens)

Lectotype, designated here: USNM 551 , the leaf originally figured as plate 28, fig. 5 by Newberry (1878), here refigured as Text-fig. 8.1, 8.2.

Leaves of this species vary from wide-ovate to trilobate with regularly spaced rounded glandular teeth and have moderately long petioles. Both Brown (1962) and McIver and Basinger (1993) assigned this species to Vitaceae . Despite similarities to Vitaceae , including the tendency for shallowly trilobate leaves, the architectural similarities with Trochodendroides are stronger. The teeth are rounded and somewhat larger than those typically seen in Trochodendroides arcticum but have the same morphology and gland position. At some localities, for example, Bison Basin, Wyoming, the leaves co-occur with an unnamed species of Nyssidium having relatively large fruits. The association of Nyssidium infructescences with leaves of Trochodendroides at some sites, and with leaves of Archeampelos at other sites, suggests that the plants producing these two leaf types were closely related.

McIver and Basinger (1993) used a broad species concept for this taxon, accommodating specimens of “ Populus ” nebrascensis NEWBERRY as well as “ Populus ” acerifolia NEWBERRY. However, Peppe (2009) documented three morphologically distinct species of Archeampelos with different stratigraphic ranges. Although McIver and Basinger’s combination Archeampelos acerifolia , based on Newberry’s original material from Fort Union, North Dakota (Text-Fig. 8), applies to many Paleocene leaf populations, for example those studied by Gemmill and Johnson (1997) from Bison Basin, Wyoming, it is inappropriate for the specimens that McIver and Basinger (1993) illustrated from the Ravenscrag Formation. Although the required new combination has not yet been published, the Ravenscrag population conforms to another widespread species of the same genus that includes the type specimen of “ Populus ” nebrascensis NEWBERRY (1868) . PEPPE (2009) documented useful morphological characters for distinguishing three species of Archeampelos that each have distinctive stratigraphic ranges in North America .

Hamamelidaceae

The leaf called Hamamelites inaequalis (NEWBERRY) R. W. BROWN was considered to be similar to extant Hamamelis virginiana L, but Brown (1962) noted that neither fruits nor seeds have been found to confirm the identification. The genus Hamamelites was erected by Saporta (1865, 1868) for leaves from the Paleocene of Sezanne, France. The leaves illustrated by Brown also resemble the extinct platanaceous genus, Platimeliphyllum MASLOVA 2002.

The infructescence illustrated by Brown (1962) as a “longitudinal hollow studded with bilobed projections” (pl. 65, fig. 44), seems likely to represent an infructescence of Hamamelidaceae . Fruiting capsules of this family will appear to have bilobed projections due to the persistence of paired styles. Unequivocal silicified fruits and of Hamamelidaceae , and their explosively dehiscent seeds, are known from the Paleocene of Almont, North Dakota ( Crane et al. 1990, Benedict et al. 2008).

Brown (1962) described Liquidambar dakotense R. W. BROWN based on winged seeds from the Anarchist Hill site in South Dakota, but he did not provide a clear justification for the generic assignment. Liquidambar seeds have a raphe along the median line of the wing, which is not present in this fossil. The other genus that Brown included in discussion of this fossil was Exbucklandia . That extant genus has seeds that are indeed very similar to this fossil. However, the seeds also fall within the range of variation of those Brown had earlier considered to be produced by Cercidiphyllum articum . In my opinion, the seed represents Nyssidium arcticum and is a part of the Trochodendroides genetrix plant.

Cucurbitaceae

Figures

Text-fig. 7. Cercidiphyllaceae 1–3. Trochodendroides genetrix (NEWBERRY) comb. nov. and associated reproductive structures (4, 5) from Killpecker Cr., Rock Springs, Wyoming (UF loc. 18126). 1. Twig with three attached leaves, showing variation in leaf shape and serration; composite figure assembled from images of both counterparts, UF 35427. 2. Complete leaf including petiole, UF 13243. 3. Same as 2, detail of venation. 4. Nyssidium arcticum (HEER) ILJINSKAYA fruits on an incomplete axis, UF 35454. 5. Dispersed winged seed, UF 35479. Scale = 3 cm in 1, 2; 1 cm in 3, 4; 0.5 cm in 5.