Koll et al.—Gigantopteridium and Cathaysiopteris taxonomy
from secondary veins at 45–60°. Tertiary veins are evenly spaced along secondary vein from which they originate, rarely branching. False suture vein produced between adjacent secondary veins by tertiary veins that closely approach those from adjacent secondary veins, but do not fuse with them.
Description.—Leaves are oblong to obovate and petiolate (Fig. 3.1, 3.6). Leaf apex is convex and rounded, whereas the base narrows slightly to become slightly acute. Leaves bifurcate once with forking occurring one-half to one-third of the length from the base (Fig. 3.1). The angle of bifurcation commonly is 45°. The margin is most often entire to erose, rarely sinuous (Fig. 3.1, 3.2, 3.5, 3.6). Specimens have three orders of venation (Fig. 3.1–3.3, 3.6, 3.7). Midvein width 1–3mm. Secondary veins are pinnate and opposite with regular spacing. The angle of attachment of secondary veins to the midvein is acute, ranging from 50–60°, all exhibiting decurrent attachment to the primary vein (Fig. 3.1, 3.6, 3.7). Secondary veins dissipate just before the margin to terminate in dichotomous branches that continue to the margin. Secondary veins termination rarely preserved in the specimens examined, however appears to terminate in the sinus or apex of the more sinuate specimens. Subsidiary and accessory intersecondary tertiary veins are present. Tertiary veins originating from primary vein at 80–90° (Fig. 3.2, 3.7). Tertiary veins originating from secondary veins are opposite and arise at an acute angle ranging from 45–60°, most commonly 45°. Tertiary veins are evenly spaced along a secondary vein, are straight to slightly arched and very rarely branched, but if branched, the branching is monopodial and occurs once at or near the point of attachment to the secondary vein. Tertiary veins from adjacent secondary veins terminate in the intersecondary space. The tertiary veins from adjacent secondary veins approach one another closely, but do not fuse, thus creating a false suture vein feature arising between any pair of adjacent secondary veins at the point where the subjacent secondary joins the midvein; the false suture vein thus is initiated a short distance from the midrib and then arches slightly to run parallel to the secondary veins, midway between them, in the intersecondary space continuing to the margin (Fig. 3.2–3.4, 3.7).
Remarks.—The concept of Gigantopteridium yochelsonii presented here includes foliar traits that were not part of the original diagnosis of Mamay (1986): (1) increased variability in margin character, formerly described as sinuous or crenate, now including specimens exhibiting entire margins; (2) a smaller range of variability and more acute angle of insertion of secondary veins at their point of origin from the primary, pre- viously 30–80° but found here to originate at 50–60°, with the angle slightly more acute distally and slightly more obtuse towards the base; (3) branching of the major secondary veins just before the margin, the vein forking to reach the margin; (4) reduced variation in the angle of insertion of the tertiary veins to the secondary veins, formerly described as ranging from 50–75°, but most commonly seen in this study to be ~ 45°; and (5) lack of a true suture vein previously described as formed through the fusion of tertiary veins from adjacent secondary veins in the intersecondary space, however, this study found that tertiary veins rarely fuse either with those from the adjacent
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secondary or with those positioned laterally adjacent, originat- ing from the same secondary. Furthermore, there is little fusion between adjacent tertiary veins even at their termination points. Thus, there is no suture vein that continues strongly from the midvein to the margin. Mamay (1986) noted a resemblance between G. yochelsonii
and the Cathaysian species, Cathaysiopteris whitei (Halle) Koidzumi, citing the presence of three orders of venation, intersecondary sutures, and the general simplicity of the higher order venation resulting from a lack of branching of the tertiary venation. Although we agree that the two species have similar foliar traits, comparison of theC. whitei literature with the diagnosis of G. yochelsonii described here as well as the establishment of another species, Gigantopteridium utebaturianum n. sp. (described below), clarifies the unique characteristics for each species, and thus provides justification to maintain their distinction (Figs. 3, 4). Mamay (1986) distinguished G. yochelsonii from C. whitei
on the basis of variation of several features: (1) the angle of insertion of secondary veins at their point of attachment to the primary vein, ranging from 30–80° in G. yochelsonii and 90° in C. whitei; (2) the angle of insertion of tertiary veins to secondary veins, 50–75° in G. yochelsonii and more acute in C. whitei (~30°); (3) secondary vein termination points, at the margin in G. yochelsonii, but just before the margin branching into dichotomously forking veins to reach the margin in C. whitei; and (4) the origination of the suture vein at the junction of the subjacent secondary and primary veins in G. yochelsonii and midway between two adjacent secondary veins directly from the primary vein in C. whitei. It can be noted, in addition to Mamay’s original observations, that C. whitei has a distinct suture vein created by the fusion of tertiary veins originating from adjacent secondary veins, which contrasts strongly with the presence of a false suture in G. yochelsonii (Fig. 3.4). We found that both G. yochelsonii and the new species
of Gigantopteridium are morphologically distinct from Cathaysiopteris. In agreement with the conclusion of Mamay (1986), this study finds the key differences distinguishing G. yochelsonii from C. whitei to be the origination point and presence or absence of the intersecondary suture, a false suture originating at the junction of the primary and lower secondary veins and arching into the intersecondary space to meet the margin in G. yochelsonii and a robust suture originating directly from the primary vein midway between two adjacent secondary veins running parallel to the margin in C. whitei, and the lack of ultimate order branching in G. yochelsonii versus a habit of two-three dichotomous branches in C. whitei. The comparison of G. utebaturianum n. sp. and C. whitei is discussed below.
Genus Gigantopteridium Koidzumi, 1934
Gigantopteridium utebaturianum new species Figure 4.1–4.8
Holotype.—USNM 597099 (USNM locality number 40042).
Paratypes.—USNM 406023, 597075, 597138, 617577, and 636752.
Diagnosis.—Leaves oblong to obovate. Margin entire to erose, occasionally sinuous. Three orders of venation. Angle of
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