Gaylussacia sp.

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 : 9

Gaylussacia sp.

Figure 2.5

Description. One simple, 2.4 cm long, 1.0 cm wide, petiolate leaf displays characteristics of Gaylussacia . The petiole is very short (~ 1 mm long) with a significant expansion near the stem. The blade is obovate, symmetrical. Margin is unlobed and entire. Base is acute, cuneate. Apex is obtuse, rounded. Primary venation is pinnate. Secondary venation is brochidodromous and decurrent. Secondaries form long and irregularly spaced loops that depart the midvein at angles of 20–30°, the angles increasing to approximately 45° distally. Tertiary venation is reticulate.

Site occurrence. Scarborough School.

Remarks. Of the approximately 50 species of Gaylussacia worldwide, most of the North American species occur on the southeastern coastal plain, including G. baccata , G. dumosa , G. frondosa ( Figure 2.6 ), G. mosieri , G. nana , and G. tomentosa . The Citronelle Formation leaf described here is the first report of fossil Gaylussacia in North America. The unique, disjunct biogeographical pattern of Gaylussacia (it is present in eastern portions of North America and South America) is most commonly explained as a probable origination in South America with subsequent migration into North America during the Paleogene via the Caribbean islands. However, molecular approaches suggest that the genus originated in North America and subsequently expanded into South America ( Floyd, 2002).

Figures

FIGURE 2. Representative Aquifoliaceae through Juglandaceae from the Citronelle Formation. 1. Ilex sp. leaf (UF 19210–062063), scale bar equals 5 mm. 2. Clethra cf. alnifolia (UF 19210–062064) partial leaf, arrow indicates mucronate tooth apex, scale bar equals 5 mm. 3. Close-up of Figure 2.2 Clethra leaf, note mixed-percurrent tertiaries, scale bar equals 2.5 mm. 4. Extant Clethra alnifolia leaf from USAM herbarium for comparison with Figure 2.2, scale bar equals 5 mm. 5. Gaylussacia sp. leaf (UF 19315–062065), scale bar equals 5 mm. 6. Extant Gaylussacia sp. from USAM herbarium for comparison with Figure 2.5, scale bar equals 5 mm. 7. Vaccinium sp. leaf (UF 19315–062066), scale bar equals 5 mm. 8. Close-up of Vaccinium leaf margin from Figure 2.7 showing teeth, scale bar equals 2.5 mm. 9. Carya fruit (UF 19315 – 062068), scale bar equals 5 mm. 10. Carya sp. catkin with in situ pollen (UF 19315 – 062067), scale bar equals 5 mm. 11. Carya sp. pollen tetrad from specimen in Figure 2.10, scale bar equals 10 µm.