Clethra cf. alnifolia Linnaeus, 1753

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

Clethra cf. alnifolia Linnaeus, 1753

Figure 2.2–2.3

Description. One partial leaf is identified as Clethra sp. , measuring 4 cm long and 2.5 cm wide. The leaf is simple, petiolate, obovate. The margin is unlobed, serrate. The base is incomplete, but was probably acute. Primary venation is pinnate. Secondary venation is semicraspedodromous and excurrent. Secondaries emerge from the midrib at approximately 45°. Tertiary veins are mixed-percurrent (both alternate and opposite percurrent); some of the opposite percurrent veins are sinuous, but most are straight. Quaternary venation is predominantly regular reticulate, occasionally irregularly reticulate. Quinternary veins are regular, reticulate. Teeth are of a single order, small, irregularly spaced, the number increasing distally. Tooth sinuses are generally round, teeth straight/convex proximally, straight/concave distally. On some teeth all that is visible is a long, mucronate apex, a characteristic common to modern forms of C. alnifolia .

Site Occurrence. Perdido Park.

Remarks. Clethra today encompasses approximately 65 species, but only three occur in North America. Clethra acuminata occurs mostly in montane woodlands. Clethra alnifolia and C. tomentosa are found at lower elevations and in wetland areas. Of these two, C. alnifolia ( Figure 2.4 ) has a wider distribution and is found mainly along the coastal plain from southern Maine to northern Florida and then westward to southeastern Texas. Fossil flowers within the core Ericales somewhat comparable to those of the Clethraceae have been found from Late Cretaceous deposits of Georgia, USA. ( Schönenberger et al., 2012). Fruits and seeds of Clethra have been described from the middle Miocene of Europe ( Friis, 1985).

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.