Platanus occidentalis Linnaeus, 1753 Leaves

Stults, DZ & Axsmith, BJ, 2015, New plant fossil records and paleoclimate analyses of the late Pliocene Citronelle Formation flora, U. S. Gulf Coast, Palaeontologia Electronica (New York, N. Y.: 1991) 2 (6), pp. 1-35 : 16-18

Platanus occidentalis Linnaeus, 1753 Leaves

Figure 6.3

Description. Ten large leaves of this species are present at the Scarborough School site, whereas five smaller, possibly less mature leaves are present at Perdido Park. The larger specimens are> 15.0 cm long and ~ 18.0 cm wide. A complete smaller specimen (part and counterpart) is 6.1 wide and 6 cm long. L:W ratios for large and smaller leaves are ~ 1:1. Margins are lobed and serrate. The larger and smaller specimens differ somewhat in morphology as also seen in the extant species. For example, the larger leaves are usually strongly five-lobed, while the smaller leaves have three shallow lobes. Small, basal lobes occur on the larger leaves. Leaf bases are either cordate or lobate, regardless of leaf size. Apices of the lobes on large specimens are acute, while apices on smaller specimens are sometimes acute, sometimes obtuse. The primary venation of the larger leaves is mostly palinactinodromous, while the smaller leaves have actinodromous primary framework. Compound agrophic veins are evident on the smaller leaves. The margins have simple teeth, with 0–2 teeth per cm. One order of teeth is present, however, tooth sizes are variable on any given leaf. Teeth are irregularly spaced on the margin (as a whole), but are regularly spaced when comparing symmetry on either side of the lobes. Sinuses between the teeth are rounded. Teeth are convex/ straight proximally, concave/straight distally.

Fruits

Figure 6.4

Description. Four Platanus fruiting heads have been found at the Red Bluff site. The most complete is 2.3 cm in diameter. Achenes with persistent styles are ~ 8 mm long and 2 mm wide. The receptacle is 9 mm wide. The fossil leaves and fruits are identical to those of the extant species P. occidentalis .

Site occurrence. Large leaves are from Scarborough School; small leaves are from Perdido Park; fruiting structures are from Red Bluff.

Remarks. Of the eight species of Platanus , three (or four) occur in North America. Platanus racemosa and P. wrightii (possibly P. racemus var. wrightii ) are found primarily in areas of Arizona, California, and New Mexico, and also in northwestern Mexico. Platanus mexicana occurs in Mexico and Guatemala. Platanus occidentalis has a wide distribution along streams and rivers in eastern North America, from southern Maine to the panhandle of Florida, westward to south-central Texas, and northward to Iowa, Wisconsin, and Michigan.

The fossil record of Platanus in North America begins in the Paleocene ( Manchester, 1999). Platanus is also present in the western Miocene Clarkia and Succor Creek floras ( Smiley and Rember, 1985; Fields, 1996). The apparent divergence of P. occidentalis from P. mexicana occurred in the middle to late Miocene ( Feng et al., 2005). Fossils of possible P. occidentalis have been reported from the Brandywine flora of Maryland ( McCartan et al., 1990).

Figures

FIGURE 6. Representative Oleaceae (continued), Platanaceae, and Roseaceae from the Citronelle Formation. 1. Fraxinus leaflet (UF 19210–062078), scale bar equals 1 cm. 2. Close-up of Figure 6.1 Fraxinus leaflet showing higher order venation, scale bar equals 5 mm. 3. Platanus occidentalis leaf (UF 19210–062079), scale bar equals 1 cm. 4. Platanus occidentalis fruit (UF 19211–062080), showing persistent style at arrow, scale bar equals 1 cm. 5. Crataegus leaf species 1 (UF19315–062081) similar to C. spatulatha, scale bar equals 5 mm. 6. Close-up of Figure 6.5 Crataegus leaf showing higher order venation, scale bar equals 2.5 mm. 7. Crataegus species #2 leaf (UF 19210–062082), wedge-shaped lamina similar to C. floridana, compare with Figure 7.1, scale bar equals 5 mm. 8. Close-up of Figure 6.7 Crataegus leaf showing higher order venation, scale bar equals 2.5 mm.