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Crenulopteris subcrenulata (Lesquereux) Wittry, comb. nov.
1866. Alethopteris crenulata (non Göppert); Lesquereux: p. 439, pl. 39, figs. 2-4
1870. Alethopteris crenulata (non Brongniart); Lesquereux: p. 392, pl. 13, figs. 14, 15
1879-80. Pseudopecopteris subcrenulata Lesquereux: p. 193, pl. 37, figs. 7, 8(?)
1879-80. Pecopteris serpillifolia Lesquereux: p. 237, pl. 46, figs. 1, 2, non fig. 3
1879-80. Pecopteris dentata (non Brongniart); Lesquereux: p. 240; pl. 44, fig. 4
1925. Pecopteris miltoni (non Artis); Noé: pl. 34, fig. 3
1958. Asterotheca crenulata (non Brongniart); Langford: p. 163, fig. 278, 9a; (?) figs. 276, 277, 278b
1963. Asterotheca crenulata (non Brongniart); Langford: p. 199, figs. 795-798
1969. Pecopteris serpillaefolia Lesquereux; Darrah: pl. 54, fig. 1
1969. Pecopteris lamuriana (non Heer); Darrah: pl. 15 figs. 3, 41969. Pecopteris hemitelioides (non Brongniart); Darrah: pl. 19, fig. 2
1979. Pecopteris serpillifolia Lesquereux; Janssen: p. 126, fig. 107
1979. Asterotheca crenulata (non Brongniart); Janssen: p. 131, fig. 115
Basionym; Alethopteris crenulata Lesquereux, 1866. Ill. Geol. Surv., Vol. 2, Report on the Fossil Plants of Illinois. p. 439 pl. 39, figs. 2-4
Lesquereux type specimens are missing and presumed lost. It had been reported (Lendemer, 2002) that the last known syntype specimen, referred to as pl. 37, fig. 7, 1879 (shown here as Fig. 2), was housed in the Harvard paleobotany collection under catalogue number HU6237. After this author examined the specimen, it was determined this was in error, and not a Lesquereux type specimen. It is proposed here that PP51104 be made the neotype and PP26770 a paratype. Both are deposited in the paleobotanical type and figured collection of The Field Museum, Chicago, Illinois, USA.
DESCRIPTION: The penultimate pinnae are linear or slightly wider near the middle, and have heavy and straight rachises (see Fig. 7). The ultimate pinnae (see Fig. 10) are linear or lanceolate and rounded at their apices. When still pinnatifid, they are slightly expanded near the base from the enlarged basal lobes. The rachis of the penultimate pinnae is channeled on the upper side, and rounded, smooth, inflated, or punctate on the lower. In the pinnules that are still entire on the penultimate pinnae (see Fig. 6 inset), the midvein extends to the tip of the pinnule and is somewhat decurrent and inflated at the base. The lateral veins are distant and generally fork once at different points along their length, then meet the margin at various angles. The vein bundles near the base of this type of pinnule are generally more developed. The lobed ultimate pinnae have "lobatopterid" venation. The veins divide once near the midvein and then the upper vein divides a second time into the middle. The midvein undulates and is strongly decurrent. Fully mature ultimate pinnae are lobed or occasionally pinnatifid. The lateral veins are alternate, simple, and irregularly arch or undulate to the margins, making no two vein patterns exactly alike. The number of lateral veins on each side of the midvein in the pinnules, or in lobes of the ultimate pinnae, is typically three or four, occasionally five. The pinnules often have surfaces appearing to be covered by minute scales when well preserved, but not heavy enough to obscure the venation. The sori are small, submarginal, and have an asterothecoid appearance with 4 or 5 sporangia.
REMARKS: Crenulopteris subcrenulata is uncommon in the Mazon Creek flora. It has been poorly understood and forms of this type have incorrectly been called Pecopteris (Cyathocarpus) arborescens (arborea), Pecopteris (Cyathocarpus) hemitelioides, or Pecopteris (Diplazites) unita.
The venation of mature C. subcrenulata appears most similar to D. unita, but can be separated by the straight and alternate pattern of the lateral veins in the former, compared with the opposite or subopposite and arcuate pattern in the latter. C. arborea has pinnules perpendicular to the rachis with straight and perpendicular mid- veins, features not seen in P. subcrenulata.
Unlike other areas, P. subcrenulata is fairly common in Mazon Creek flora and all of its growth stages can be readily found. Starting with Fig. 3, an example of the most-distant pinna, Figs. 3 through 9 are ordered as they would have been seen growing down from the frond tip when alive. Fig. 10 shows how the penultimate pinnae developed along a short sec- tion of the frond. Fig. 11 is one of the very rare known examples of a fertile P. subcrenulata.
P. subcrenulata grew into very large fronds displaying a great amount of variability. Lesquereux did not recognize the extent of this variation and simultaneously described Pecopteris subcrenulata and Pecopteris serpillifolia, not realizing two of the three P. serpillifolia syntypes were growth forms of P. subcrenulata. The two syntypes USNM 13929 and USNM 13930 are removed here as syntypes for P. serpillifolia. The third syntype USNM 13931 remains under P. (Cyathocarpus) serpillifolia as the holotype.
The features of C. subcrenulata necessitate its removal from Pecopteris. The sori most resemble those of the marattialean ferns. The well-documented Palaeozoic marattialean ferns, with mostly crenate or lobed mature pinnae and "lobatopterid" venation, are now accommodated in Crenulopteris.
From Wittry's "A Comprehensive Guide to the Fossil Flora of Mazon Creek".
