Citrophyllum aligera Lesquereux, 1892

Wang, Hongshan & Dilcher, David L., 2018, Early Cretaceous angiosperm leaves from the Dakota Formation, Hoisington III locality, Kansas, USA, Palaeontologia Electronica (34 A) 21 (3), pp. 1-49 : 32

Citrophyllum aligera Lesquereux, 1892

Figure 20

*1892 Ficus aligera Lesquereux , p. 84, pl. 10, figs. 3-6.

*1909 Citrophyllum aligerum (Lesquereux) Berry : Berry, p. 258, pl. 18a, figs. 1-8.

*1911a Citrophyllum aligera (Lesquereux) Berry : Berry, p. 169, pl. 21, figs. 1-8.

Emended specific diagnosis. Leaf simple, whole lamina and base symmetrical. Apex obtuse. Margin entire. Petiole aliform, base inflated; demarcation between lamina wing and lamina distinct. Primary venation pinnate; primary vein stout, course straight. Secondary venation festooned brochidodromous; secondary veins thin relative to primary vein, subopposite to alternate; angle of divergence moderate acute; secondary veins uniformly curved, joining exmedial branches of superadjacent secondary vein at right or obtuse angles to form two series of loops. Intersecondary veins common, simple. Tertiary veins random reticulate, but tending to be percurrent near leaf margin. Quaternary and quinternary veins random reticulate.

Description. Leaf simple, whole lamina and base symmetrical. Form ovate to narrow elliptic, L / W 1.3 to 2.6, lamina 3 to 6 cm wide and 8 cm long. Apex obtuse. Base normal obtuse or cuneate. Margin entire. Petiole aliform, base inflated; petiole 0.5 to 1.8 mm wide and 2.5 cm to 4 cm long; lamina wing 0.2 mm to 1.8 mm wide on each side; demarcation between lamina wing and lamina distinct. Primary venation pinnate; primary vein stout, 0.5 mm to 1 mm wide, course straight. Secondary venation festooned brochidodromous; secondary veins thin relative to primary vein, ca. nine pairs per leaf lamina, subopposite to alternate; angle of divergence moderate acute (ca. 50º), with lowest pair more obtuse than pairs above; secondary vein uniformly curved, joining exmedial branches of superadjacent secondary vein at right or obtuse angles to form two series of loops. Intersecondary veins common, one to two between adjacent secondary veins, simple, extending a distance of one third to one half of half lamina. Tertiary veins random reticulate, but tending to be percurrent near leaf margin. Quaternary and quinternary veins random reticulate.

Number of specimens examined. 6.

Neotype (designated here). UF15706-24646 ( Figure 20.1 ).

Other specimens illustrated. UF 15706-24645 ( Figure 20.2 ); 24332 ( Figure 20.3-4 ).

Remarks. Citrophyllum aligera differs from Citrophyllum doylei , a species established by Upchurch and Dilcher (1990, p.43-45, plate 27, figures 1, 3, 4; text-figure 21), in having a longer petiole and festooned brochidodromous secondary venation. Some specimens from the Hoisington III locality occasionally don’t have alate petioles. These specimens may represent the further reduction of lamina tissue on the petiole.

The genus Citrophyllum was established by Berry (1909) to accommodate fossil leaves with elliptical to ovate or ovate-lanceolate, coriaceous leaves, with entire or slightly undulate margins and stout conspicuously alate petioles. These characters are generally similar to those of the modern genus Citrus . Berry (1909, p. 258) transferred Lesquereux’s (1892) Dakota specimens, originally assigned to the extant genus Ficus , to Citrophyllum . As discussed by Upchurch and Dilcher (1990, p. 44), the modern affinities of the genus Citrophyllum is with Sapindales instead of Rutaceae because it doesn’t possess features that characterize Rutaceae . Leaves of Rutaceae have been reported only from the Cenozoic of Asia (Guo, 2011; Xie et al., 2013) and Africa (Pan, 2010), but no Rutaceae fossils have been found from the Cretaceous.

Figures

FIGURE 20. Citrophyllum aligera Lesquereux, 1892. 1, UF15706-24646, base of leaf showing lamina wing on petiole. Scale bar equals 5 mm. 2, UF15706-24645, base of leaf showing a long petiole with lamina wing and inflated petiolar base. Scale bar equals 5 mm. 3, UF15706-24332. leaf with a long petiole with thin lamina wing and inflated petiolar base. Scale bar equals 1 cm. 4, Enlargement of an area in Figure 20.3 (indicated by arrow) to show looping marginal veins. Scale bar equals 1 mm.