Wingia expansolobum (Upchurch and Dilcher) Wang & Dilcher, 2018

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 : 34-38

Wingia expansolobum (Upchurch and Dilcher) comb. nov.

Figures 21-23

Basionym. Dicotylophyllum expansolobum Upchurch and Dilcher (1990, p. 48-49, plate 31, text-figure 25).

Specific diagnosis. Leaf simple, irregularly five-lobed, margin toothed near apex of lobes, serrations minute, simple. Petiole long and thin, enlarged both distally and proximally. Primary venation basal actinodromous. Secondary venation predominately brochidodromous or semicraspedodromous when margin is toothed near apex; typically, one series of loops present in the excostal region if margin is entire; secondary veins below sinus and between adjacent primary veins forming inverted ‘V’ pattern. Intersecondary veins common, composite. Tertiary and quaternary veins orthogonal reticulate, forming predominately quadrangular meshes.

Description. Leaf simple, five-lobed, lamina varies from 3.2 cm long and 6 cm wide to 15 cm long and 15 cm wide; sinus deep, extending 75% to 80% of distance from apex to lamina base; medial lobe narrow obovate, narrow ovate or narrow oblong, symmetrical; lateral lobes asymmetrical, shape irregular, curved apically; outer lobes occasionally underdeveloped (leaf tending to be trilobate); apex of lobes obtuse; base of lamina obtusely cuneate or strongly rounded to give a truncate appearance; margin toothed near apex of lobes, strongly reinforced; sinus rounded, bracing accomplished by two secondary veins originated from adjacent primary veins, these two veins join and then fork to run along the margin; serrations minute, simple; serration type ranging from concave to straight on apical side and straight to convex on basal side, spacing irregular; typically three veins entering a tooth, medial vein originating form exmedial side of secondary vein, basal vein tertiary in order and running very close to the margin before entering the tooth, vein of apical side not well developed. Petiole long, thin, 8 cm long and 1 mm wide; pulvini (lower and upper) present; upper pulvinus extending up to 1 cm proximally along the petiole. Primary venation basal actinodromous; primary veins stout to massive, multi-stranded; medial primary vein straight in course; inner lateral primary veins apically curved; outer primary veins apically curved or recurved. Secondary venation predominately brochidodromous or occasionally semicraspedodromous near apex; secondary veins thin relative to primary veins; originating from primary veins at wide acute angles, straight or slightly curved and then abruptly curved very close to the margin to join superadjacent secondary veins to form rectangular or rhomboidal intercostal regions; typically one series of loops present in the excostal region if margin is entire; secondary veins below sinus and between adjacent primary veins forming inverted ‘V’ pattern. Intersecondary veins common, composite, one to three per intercostal region. Tertiary veins orthogonal reticulate, forming predominately quadrangular meshes, tending to be percurrent and arranged at very oblique angles (<20º) with primary veins. Quaternary veins orthogonal reticulate. Veins of higher order not observed.

Number of specimens examined. 52.

Holotype. UF15713-8304 (designated by Upchurch and Dilcher, 1990).

Specimens illustrated. UF 15705-30158 ( Figure 21.1-3 ); 24788 ( Figure 21.4 ); 14825 ( Figure 22.1- 2 ); 24461 ( Figure 22.3-4 ); 14828 ( Figure 23.1-3 ).

Remarks. This species was established by Upchurch and Dilcher (1990) based on one specimen from the Rose Creek I locality, Nebraska. We emend the specific diagnosis because specimens from the Hoisington III locality yield more information on the leaf features, especially the variations of leaf morphology. For example, secondary venation of Wingia expansolobum can vary from predominately brochidodromous to semicraspedodromous. High order venation (tertiary and quaternary veins) is well preserved on the specimens from the Hoisington III locality, Kansas.

The proximal and distal enlarged areas on the petioles of Wingia expansolobum leaves may be pulvini. In extant plants, the pulvinus, a motor organ for leaf movement (regulating leaf position), is often found in the Fabaceae (Satter and Morse, 1990; Rodrigues and Machado, 2008). A search using a subset of characters (vegetative morphology and anatomy: leaves [form]) in Intkey (Dallwitz et al., 1995) and using two characters (pulvinate and well-developed leaves) of Wingia expansolobum resulted in 11 families ( Averrhoaceae , Barbeuiaceae , Empetraceae , Lardizabalaceae, Leguminosae , Marantaceae , Santalaceae , Sapindaceae , Staphyleaceae, Umbelliferae , and Zygophyllaceae ) that have pulvinate leaves. When more characters (including leaf petiolate, simple, palmately-lobed, and primary vein palmate and in this order) are used, only two families, Leguminosae and Umbelliferae, remain. Both families do not seem to have similar leaf morphology as that of Wingia expansolobum . As indicated by Upchurch and Dilcher (1990), no extant species of Magnoliidae has five-lobed organization with basally palmate (actinodromous) primary venation. The modern affinities of Wingia expansolobum remain indeterminate but future collection of specimens with cuticular material may help clear this uncertainty.

Many recent discoveries of the Early Cretaceous fossil leaves with similar tooth pattern have been proposed to be related to the Eudicots. For example, Iterophyllum lobatum Barral et al. (Ranucuales; Barral et al., 2013) is a fossil species based on leaves from the late Barremian of Las Hoyas, Spain. The simple leaf is petiolate and pinnately lobed with chloranthoid-like glands at the lobe apices and the sinuses. Fairlingtonia thyrsopteroides (Fontaine) Jud (Jud, 2015) and Vernifolium tenuiloba Jud and Sohn (Jud and Sohn, 2016) from the Early Cretaceous Potomac Group in Maryland and Virginia, USA were also placed within the Eudicot clade, although their familial and ordinal affinities are unknown.

Figures

FIGURE 21. Wingia expansolobum (Upchurch and Dilcher) comb. nov. 1, UF15706-30158a, specimen showing a complete leaf. Note the long petiole with a swollen base and the extension of lamina tissue on the petiole. Scale bar equals 1 cm. 2, Enlargement of the petiole in Figure 21.1 to show the swollen base. Scale bar equals 2 mm. 3, UF15706-30158b, enlargement of a leaf on the back of the same specimen to show high order venation and glandular teeth. Scale bar equals 3 mm. 4, UF15706-24788, specimen showing a deeply lobed leaf. Note apically curved outer lateral lobes. Scale bar equals 1 cm.

FIGURE 22. Wingia expansolobum (Upchurch and Dilcher) comb. nov. 1, UF15706-14825, specimen showing a large leaf with irregular shape of lateral lobes. Note the structurally reinforced margin on sinus, pluvinus lamina extension on the thin and long petiole. Scale bar equals 1 cm. 2, Enlargement of Figure 22.1 to show the pluvinus lamina extension on the petiole. Scale bar equals 2 mm. 3, UF15706-24461, enlargement of Figure 22.4 (area indicated by arrow) to show looping of secondary veins near the lamina margin. Scale bar equals 1 mm. 4, UF15706-24461, specimen showing a small leaf. Scale bar equals 5 mm.

FIGURE 23. Wingia expansolobum (Upchurch and Dilcher) comb. nov. 1, UF15706-14828, specimen showing a multi-lobed leaf. Scale bar equals 1 cm. 2, Enlargement of Figure 23.1 (area indicated by the upper arrow) to show secondary and tertiary venation. Scale bar equals 1 mm. 3, Enlargement of Figure 23.1 (area indicated by the lower arrow) to show venation near the lamina margin. Scale bar equals 2 mm.