Nordenskioeldia borealis HEER

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

Nordenskioeldia borealis HEER

Nordenskioeldia borealis HEER ( Brown 1962, pl. 67, figs 13, 45) was widely distributed in the late Cretaceous and Paleocene of the Northern Hemisphere and is represented at numerous localities of the Rocky Mountains and Great Plains region. This genus and species was reviewed in detail by Crane et al. (1991) and Wang et al. (2009). It is known from infructescences, whole fruits, dispersed fruitlets, and shed seeds. The seeds, which were figured and described as “seeds with papillose inner surface” by Brown (1962, Pl. 67, figs 9, 10, 14–16, 22, 23), are known to belong to this extinct genus because one is shown dispersing from a fruitlet in figs 28, 29 of Crane et al. (1991), and they are preserved in situ with fruits of the silicified specimens from Almont, North Dakota ( Crane et al. 1991, figs 16, 28). Nordenskioeldia associates with the same kind of extinct leaf in the Late Cretaceous to Paleocene of the Northern Hemisphere, and even in the Miocene refugial populations ( Manchester et al. 1991). Leaves of Zizyphoides SEWARD et CONWAY in the Paleocene of North America have been called Z. flabella (NEWBERRY) CRANE , MANCHESTER et DILCHER; the holotype is from the Chuckanut Formation of west coastal Washington.

Cercidiphyllaceae

Text-figs 7 , 8

Brown (1939b, 1962) called attention to the co-occurrence of leaves, fruits, and winged seeds resembling extant Cercidiphyllum at numerous Paleocene and Eocene sites in North America. He assigned the fossils to the extant genus, collectively as Cercidiphyllum arcticum (HEER) R. W. BROWN although he noted that the fruits differ from those of extant species in the genus in having more prominent transverse and diagonal striations, and are borne on racemose rather than clustered inflorescences (e.g., Text-fig. 7.4 ). In a comparative study of similar leaves from the Paleocene of England, Crane (1984) applied separate fossil-generic names, Trochodendroides BERRY for leaves and Nyssidium HEER for the fruits. The same kind of infructescences were documented in detail from the Paleocene of Asia ( Feng et al. 2000). The Joffre Bridge locality of Alberta yielded such leaves, fruits, and seeds in association with both pistillate and staminate inflorescences, twigs showing phyllotaxy, and young seedlings, providing an especially complete reconstruction of the plant named Joffrea spiersii ( Crane and Stockey 1985) .

Brown had inadvertently included multiple kinds of leaves in his concept of fossil Cercidiphyllum arcticum foliage ( Hickey 1977). Some, usually with evenly serrate margins, belong to Trochodendroides and presumably correspond, as he surmised, with the fruits he described and illustrated (ie., Nyssidium arcticum (HEER) ILJINSKAYA sensu Crane 1984 ). Other leaves (e.g., Brown 1930b, plate 53, figs 3–5) with irregular crenations and/or sometimes entiremargins are consistently found in co-occurrence with fruits of another extinct fruit genus, Nordenskioeldia HEER ( Crane et al. 1991) . These were subsequently treated as “ Cocculus” flabella (NEWBERRY) J. WOLFE (1966) , Menispermites parvareolatus HICKEY (1977) , and then, using the oldest available generic name, collectively transferred to Zizyphoides flabella (NEWBERRY) CRANE, MANCHESTER et DILCHER (1991) . These leaves are discussed herein along with Nordenskioeldia borealis . Although the organs have not been found in mutual attachment, they co-occur at numerous sites of late Cretaceous and Paleocene age throughout the Northern Hemisphere, and even in Miocene refugial populations ( Manchester et al. 1991).

Even from the first recognition of the species described as Populus arctica by HEER from Greenland, the species concept included variation ranging from entire-margined and irregularly crenate leaves now thought to coincide with Nordenskioeldia fruits, as well as those with more regularly spaced crenations believed to represent the Nyssidium plant. As noted by Budantsev and Golovneva (2009), the lectotype of Populus arctica HEER (basionym of Trochodendroides arctica (HEER) BERRY ) resembles the leaves treated by Crane et al. (1991) and Manchester et al. (1991) as Zyziphoides. Thus, it is possible that the type species of Trochodendroides arctica (HEER) BERRY coincides with the Nordenskioeldia plant, rather than with the Nyssidium plant to which it has often been associated. To avoid further confusion, I hesitate to use the epithet arctica , based on Greenland material, for the North American taxa representing this group.

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.