Pabiania variloba Upchurch and Dilcher, 1990

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 : 12

Pabiania variloba Upchurch and Dilcher, 1990

Figures 7-8

v. 1981a Acerites multiformis Lesquereux ; Retallack and Dilcher, 1981a, p. 38, fig. 2.4.

Description. Leaf commonly trilobate, rarely bilobate or unlobed; base ranging from acute to obtuse and tending towards cuneate, with the basalmost portion of the lamina decurrent on the petiole; margin entire; apex of lobes acute to rounded; unlobed leaves broad elliptic to obovate, with rounded apex. Primary venation basal to suprabasal actinodromous in 3-lobed leaves, pinnate in unlobed leaves; midvein moderate; lateral primary veins similar to midvein in thickness, at lower angle than superadjacent secondary veins and tending to be recurved, commonly decurrent on midvein, producing one to three festooned brochidodromous external branches. Secondary venation festooned brochidodromous; secondary veins thin or moderate relative to primary veins, three to six pairs along midvein, with one pair of basilaminar secondary veins present in all leaves, alternate, moderate acute, straight to apically curved, tending to be festooned brochidodromous except near sinuses. Tertiary venation reticulate; tertiary veins thin relative to secondary veins, opposite to alternate, closely but somewhat irregularly spaced, originating at acute to right angles. Quaternary venation intergrading with tertiary veins, generally unbranched; quaternary veins opposite to alternate, non-orthogonal, enclosing somewhat elongate, 4-sided regions. Quinternary venation highly irregular, both ramified and reticulate, arising both from thick lateral branches of the quaternary veins and from the sides of lower order veins; quinternary veins weak, curved, often producing branches to form an open venation. Areolation poorly developed. Marginal venation consisting of a thin fimbrial vein.

Number of specimens examined. 90.

Specimens illustrated. UF 15706-24423 ( Figure 7.1-3 ); 30154 ( Figure 7.4-5 ); 14832 ( Figure 7.6 ); 14823 ( Figure 8.1 ); 24464 ( Figure 8.2, 8.4 ); 24587 ( Figure 8.3 ).

Occurrences. Rose Creek locality, Nebraska and Hoisington III locality, Kansas.

Remarks. In Upchurch and Dilcher’s (1990) diagnosis and description of this species, the primary venation was described as palinactinodromous. Observations based on Hoisington III locality specimens indicate that the primary venation of P. variloba can vary from basal actinodromous ( Figure 8.1 ), suprabasal actinodromous ( Figure 7.6 ), to suprabasal palinactinodromous ( Figure 7.1-3 ). The leaves from the Rose Creek locality, Nebraska described by Upchurch and Dilcher (1990) and stored at the Paleobotany collection in the Florida Museum of Natural History (more than 100 specimens) are smaller in size compared with the specimens from the Hoisington III locality, Kansas. The specimens from the Hoisington III locality also show that the petioles are long and they have winged lamina tissue along both sides. The petiole base may be ocreate ( Figure 7.4, 7.5 ). Other variations of leaf morphological characters include: (1) lamina from unlobed ( Figure 8.3 ) to trilobed ( Figures 7.1, 7.6 , 8.1-2 ); leaf base from acute ( Figure 7.6 ) to rounded ( Figure 8.1 ); (2) apex of lamina lobes from acute ( Figure 7.6 ), rounded ( Figure 7.1 ), to mucronate ( Figure 8.2 ). All other leaf morphological characters are consistent with those described by Upchurch and Dilcher (1990).

Heer (1883, plate 38, figure 3) and Lesquereux (1892, plate 54, figures 1-3) described a few specimens with similar leaf morphology and assigned them to Aralia groenlandica Heer. Unfortunately , only primary and secondary venation are observed on these leaves, which makes it difficult to compare them with the specimens from the Rose Creek and Hoisington III localities.

Figures

FIGURE 7. Pabiania variloba Upchurch and Dilcher, 1990. 1-3, UF15706-24423, specimen showing suprabasal actinodromous primary venation (scale bar equals 1 cm) (1), enlargement of a sinus area to show sinus bracing by secondary veins (scale bar equals 2 mm) (2); and enlargement of basal portion of leaf to show two pairs of basal secondary veins (scale bar equals 2 mm) (3). 4-5, UF15706-30154, specimen showing a long petiole and ocrea-like structure at the base (scale bar equals 5 mm) (4) and enlargement of the petiole to show the ocrea-like structure (scale bar equals 2 mm) (5). 6, UF15706-14832, specimen showing suprabasal actinodromous primary venation and acute apices of the lobes. Scale bar equals 1 cm.

FIGURE 8. Pabiania variloba Upchurch and Dilcher, 1990. 1, UF15706-14823, leaf showing basal actinodromous primary venation and basal secondary veins. Scale bar equals 1 cm. 2, UF15706-24464, leaf showing rounded lobe apex. Scale bar equals 1 cm. 3, UF15706-24587, specimen showing a small lobe on the left and entire margin on the right of the leaf. Scale bar equals 5 mm. 4, Enlargement of Figure 8.2 to show straight primary vein extending to lobe apex and two series of loops in the excostal region. Scale bar equals 1 mm.