Macginitiea nobilis (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 : 163

Macginitiea nobilis (NEWBERRY) comb. nov.

Text-figs 5.1–5.3

1868 Platanus nobilis NEWBERRY, Lyceum Nat. Hist. New York Ann., 9, p. 67. (basionym).

1898 Platanus nobilis NEWBERRY, U. S. Geol. Surv. Monogr. , 35, p. 106, pl. 34.

Lectotype, here designated: USNM 1070 . Originally figured by Newberry (1898, pl. 34), here refigured as Text-fig 5.2 , from near Fort Clark , North Dakota.

The synonymies of Platanus nobilis provided by Brown (1962) and Hickey (1977) included both trilobate and pentalobate leaves but I reserve this epithet for primarily 3-lobed leaves of Macginitiea , whereas the deeply 5-lobed leaves mentioned above belong to M. gracilis . Among the originally described specimens of M. nobilis from near Fort Clarke, North Dakota, some have only three lobes, and others have five lobes, of which the middle three greatly dominate ( Text-fig. 5.1, 5.2 ).

The Paleocene (Tiffanian) flora of Joffre Bridge, Alberta, is particularly informative, showing a range in leaf morphology for this species, including seedlings documenting early leaf development, as well as mature, trilobate leaves ( Pigg and Stockey 1991). Lobes of the lamina vary from mostly entire-margined, to mostly serrate, and a basilaminar lobe extending proximally from the junction of petiole and lamina, is usually absent, but sometimes present (e.g., Pigg and Stockey 1991, pl. 1, fig. 2; Brown 1962, pl. 29, figs 1, 3). Pigg and Stockey (1991) refrained from naming their foliage, but Maslova (2008) concluded that it conformed to P. nobilis and made the argument that this species should belong to Macginitiea : “on the one hand, morphologically similar leaves of Macginitiea and Platanus nobilis (which include transitional forms) are associated with the same reproductive structures and, on the other hand, leaves of P. nobilis , which are assigned to the extant genus, co-occur with inflorescences and infructescences essentially distinguished from those of the plane tree. This probably supports the assignment of these leaf remains to the genus Macginitiea ; however, this necessitates further detailed examination.” ( Maslova 2008, p. 1399). The narrow angle between adjacent primary veins also supports the assignment to Macginitiea . I hereby emend the generic diagnosis of Macginitiea to indicate that the number of lobes on the lamina may vary from 3 to 9. The number of lobes was not specified in the original diagnosis of Wolfe and Wehr (p. 224, 225 in Manchester 1986).

Also present at the Joffre Bridge locality are nearly complete staminate axes with up to 12 pedicellate heads ( Platananthus speirsae PIGG et STOCKEY ) having longpedunculate heads with well preserved tricolpate reticulate pollen closely matching extant Platanus pollen morphologically in both SEM and TEM ( Pigg and Stockey 1991, pl. 4, 5), plus fruiting axes bearing at least 7 pedicellate heads ( Macginicarpa manchesteri PIGG et STOCKEY ). The correlation between Macginitiea foliage, Macginicarpa infructescences and Platananthus inflorescences was also found at Eocene locations in California, Oregon, and Wyoming ( Manchester 1986).

Macginicarpa fruiting material consists of a racemose axis bearing numerous pedunculate, globose heads ( Text-fig. 4.4 ), each composed of numerous florets of five apocarpous fruits each ( Text-fig. 4.6 ), differing from extant Platanus by the lack of dispersal hairs on the individual fruits and by a prominent perianth ( Manchester 1986). In addition, the staminate flowers, with similarly well-developed perianth, had the unique characteristic that the five stamens of each floret were apically connected by intertwining connective hairs, resulting in the shedding of 5-stamen units, in contrast to the shedding of single stamens in other genera of the family ( Manchester 1986). Such dispersed stamen units, now called Macginistemon mikanoides (MACGINITIE) MANCHESTER, were figured from Paleocene sites by Brown (1962, pl. 68, figs 27–29) as “pedicellate flowers or fruits,” and by Pigg and Stockey (1991, pl. 4, figs 8, 9) as “isolated group of stamens,” and “disagregating stamen inflorescence.”

Staminate inflorescences earlier called Sparganium stygium HEER from Seven Mile Creek, Montana ( Text-fig. 5.4 ; Ward 1887, pl. 3, fig. 7, showing at least ten heads on a raceme) also represent Platananthus speirsae . From the same site, the specimens that Brown (1962, pl 14, fig. 5) called Sparganium antiquum (NEWBERRY) BERRY correspond to Macginicarpa manchesteri PIGG et STOCKEY (1991) . The same location produced mainly large trilobate leaves of the M. nobilis kind (Pl. 41, fig. 1 of Ward 1885b).

Figures

Text-fig. 5. Platanaceae 1–3. Macginitiea nobilis (NEWBERRY) comb. nov. 1. This specimen is labeled as corresponding to Newberry 1898, pl. 50, fig. 1 although it does not match the published drawing exactly. From near Fort Clark, North Dakota, USNM 6964. 2. Lectotype from Newberry (1898, pl. 34), from near Fort Clark, North Dakota; composite picture assembled from images of both counterparts. USNM 1070. 3. Trilobed leaf from Seven Mile Creek, Montana (orig. figured as Platanus nobilis NEWBERRY by Ward 1886, pl. 41, fig. 1). USNM 4093. 4. Platananthus speirsae PIGG et STOCKEY axis with at least 9 attached pedunculate staminate inflorescences (arrows), Seven Mile Creek, Montana (orig. Ward 1885b, pl. 32, fig. 7), USNM 4225. Scale bars 5 cm.

Text-fig. 4. Platanaceae 1–3. Macginitiea gracilis (LESQUEREUX) J. WOLFE et WEHR leaves and associated reproductive structures 1. Holotype of Aralia gracilis LESQUEREUX from Bridger Pass, Wyoming, USNM 330. 2. Specimen showing the typical configuration of five lobes, Killpecker Creek flora, Wyoming. UF 18126-13242. 3. Silicified M. gracilis leaf from Almont, North Dakota; arrow indicates adjacent Macginicarpa infructescence, UF 15722-29202a. 4. Macginicarpa infructescence from Almont, UF15722-35493. 5. Platananthus sp., Almont, UF 15722-62019. 6. Macginicarpa glabra MANCHESTER infructescence, enlarged from fig. 3, UF 15722-29202b. Specimens in figs 3-6 collected and donated by John Curtis. Scales = 1 cm. Images 3–6 light-dark inverted.