Scripta Geologica, 07 (Special Issue 2010)
The Early Jurassic male ginkgoalean inflorescence Stachyopitys preslii Schenk and its in situ pollen
J.H.A. van Konijnenburg-van Cittert
Keywords: Ginkgoales, male inflorescence, in situ pollen, Early Jurassic, Germany.
An early Liassic male inflorescence of Stachyopitys preslii with in situ pollen is described from a clay lens in the sandpit Küfner near Pechgraben, Bavaria, Germany. These male inflorescences have been known since the 19th century and are rather common in the early Liassic floras of Bavaria, but in situ pollen was hitherto unknown. Stachyopitys preslii is always found in association with the leaves and the female fructifications of Schmeissneria microstachys. The in situ pollen proved to be monosulcate, a pollen type commonly occurring in the Cycadophyta and Ginkgophyta. This strengthens the possible attribution of the parent plant of S. preslii (Schmeissneria microstachys) to the Ginkgoales.
Schenk described Stachyopitys preslii as a genus and species for associated male and female inflorescences from the early Liassic of Bavaria (Germany) in 1867. The males consist of pedunculate axes with lateral branches. These lateral branches bear a cluster of spreading pollen sacs at their apex. The female fructifications (formerly named Pinites microstachys Presl) also consist of a pedunculate main axis, the upper part of which is covered with spirally arranged cupulate ovules, often in pairs. Over time, Stachyopitys preslii was re-interpreted as a male fructification only (Schenk, 1890, was the first to do this), probably belonging to the Ginkgoales. In particular, Baiera muensteriana was named as its possible parent plant (e.g., Gothan, 1914; Weber, 1968). In 1992 Wcislo-Luraniec described a cupulate axis of Stachyopitys preslii indicating that the species was indeed a mixture of male and female fructifications. However, she did not remove the female fructifications from S. preslii. In the same year, Kirchner (1992) doubted the attribution of Stachyopitys preslii to Baiera muensteriana because of the absence of Baiera leaves in the type locality Veitlahm (near Kulmbach) of Stachyopitys preslii.
Kirchner & van Konijnenburg-van Cittert (1994) separated the female fructifications from the male ones and named the former Schmeissneria microstachys (Presl) Kirchner et van Konijnenburg-van Cittert; these had been found attached to short shoots also bearing a tuft of undivided leaves. The attribution of these female fructifications was with the Ginkgoales although the seeds appear to be winged when mature, a feature not occurring in this group. They considered Stachyopitys preslii to be the male fructification belonging to Schmeissneria microstachys, but, as it was only found in association and not attached, the name S. preslii was retained. Although S. preslii is not uncommon in Liassic localities especially in Bavaria (Germany), but also in coeval layers in Poland (Wcislo-Luraniec, 1992), in situ pollen had previously never been recovered.
This paper describes in situ pollen from a male cone of S. preslii from the sandpit Küfner near Pechgraben (Bavaria, Germany) for the first time; its monosulcate pollen is in accordance with a possible ginkgoalean affinity.
Materials and methods
The specimen comes from the sandpit Küfner near Pechgraben (Bavaria, Germany). Stachyopitys preslii is quite common in some of the clay lenses in the sandpit, and is always found associated with leaves and female fructifications of Schmeissneria microstachys (for more details, see Kirchner & van Konijnenburg-van Cittert, 1994). The in situ pollen was prepared by macerating a pollen sac in a solution of KClO3 in 30 % HNO3 and, after thorough rinsing in water, neutralizing it in 5 % KOH. Macerated pollen was mounted on a slide in glycerine jelly and sealed with paraplast. The pollen grains were only studied under light microscopy. The specimen is stored at the Laboratory of Palaeobotany and Palynology, Utrecht, the Netherlands, under number 23116 (pollen slide 200).
Description of the male inflorescence and its in situ pollen
Description – The specimen (nr. 23116) is an incomplete inflorescence (the base is missing), consisting of a striate main axis, 23 mm long, with irregularly placed branches 1-2 mm long, each ending in a cluster of pollen sacs (Pl. 1, figs. 1, 2). The maximum number of pollen sacs observed in a cluster is eight. Pollen sacs are just over 1.0 mm long and 0.5 mm wide. The pollen was slightly immature as it was yielded in large masses (Pl. 2, figs. 1, 2) and was difficult to separate. Pollen is monosulcate, with a narrow sulcus without a margo (Pl. 2, figs. 3, 4). Mean length of pollen is 49 µm, mean width 26 µm. The wall appears to be granulate (Pl. 2).
Discussion – A couple of specimens in the Utrecht collection (e.g., 10604 A-D, Pl. 1 figs. 3, 4) also yielded a few in situ pollen grains, but only 23116 gave a large mass of slightly immature grains. It proved to be impossible to separate individual pollen grains from each other, but the pollen morphology is clear from the grains on the edges of the pollen masses (Pl. 2). As it was the only specimen yielding in situ pollen, no SEM or TEM study was undertaken.
General discussion and comparison with other Stachyopitys species
Ginkgoalean inflorescences with in situ pollen are scarce in the fossil record. The present inflorescence is the oldest male cone with a putative ginkgoalean affinity. The best known male Ginkgo with in situ pollen is the male catkin attributed to Ginkgo huttonii from the Middle Jurassic of Yorkshire (Van Konijnenburg-van Cittert, 1971, 1972; Harris & Millington, 1974). Here, the inflorescence consists of a main axis with loosely arranged short appendages, which bear two pollen sacs at their apex; thus, they differ mainly from S. preslii in the number of pollen sacs on each appendage. The pollen grains (29-42 µm in length) are monosulcate, but the pollen wall appears to be less clearly granulate than in S. preslii. The Lower Cretaceous Ginkgo liaoningensis carried 2-4 pollen sacs on each appendage and the pollen is again monosulcate; however, no details on the pollen wall morphology have been published (Liu et al., 2006). The male cones of living Ginkgo biloba have two pollen sacs on each appendage in the catkin and the pollen (34-46 µm long) is again monosulcate with a slightly granulate pollen wall (Van Konijnenburg-van Cittert, 1971). Thus, the in situ fossil and extant ginkgoalean pollen grains are remarkably similar.
Stachyopitys specimens are rare in the fossil record. Apart from the type species, S. preslii, known from Germany and Poland, Turutanova-Ketova (1931) described Stachyopitys sp. from the Jurassic of Kyrgyzstan, but no details can be observed from the illustrations other than that it looks like a Stachyopitys inflorescence. Ye Meina et al. (1986) mentioned Stachyopitys sp. from the lowermost Liassic of China, but did not describe or figure it. Schweitzer & Kirchner (1995) described Stachyopitys venustus from the Liassic of Iran. The number of pollen sacs at the end of each appendage is 6-10. The length of these pollen sacs is only up to 0.7 mm and thus is distinctly shorter than in S. preslii; this is, according to the authors, the only obvious difference between the two species. No pollen was recovered from S. venustus and no possible parent plant has been indicated other than a ginkgoalean affinity.
Anderson & Anderson (2003) described six Stachyopitys species from the Late Triassic Molteno Formation of South Africa. These species differ mainly in size of the inflorescences, with S. matatilongus as the longest (an incomplete inflorescence was almost 140 mm long); number of pollen sacs attached to the appendages (from 3-4 up to >20 for S. lacrisporangia); and shape and size of the pollen sacs (S. rotundisporangia has spherical pollen sacs, the other species all have elliptical pollen sacs). One specimen of Stachyopitys lacrisporangia was found attached to a bulbous short shoot, together with a leaf of Sphenobaiera africana (Sphenobaiera is a ginkgoalean leaf morphogenus differing from Schmeissneria in its dichotomously divided lamina). None of these Stachyopitys species yielded any pollen grains and all species had larger pollen sacs than those of Stachyopitys preslii. Holmes & Anderson (2007) recorded two of these species (S. matatilongus and S. lacrisporangia) with a cf. determination from the Middle Triassic Nymboida Coal Measures.
The type of pollen found in situ in S. preslii (the type species of the genus Stachyopitys) is of a general type found in extinct and living Ginkgophyta and Cycadophyta. No definite taxonomical attribution can be deduced from this type of pollen grains, except that it does not contradict a ginkgoalean affinity of the pollen organ. Pollen organs with a cycadophyte affinity (Cycadales or Bennettitales) are rather different in gross morphology from Stachyopitys material. Hence, a ginkgoalean affinity seems the most likely for this type of inflorescences and confirms the suggestions made by all authors describing this genus (Schenk, 1867, 1890; Gothan, 1914; Weber, 1968; Wcislo-Luraniec, 1992; Kirchner, 1992; Kirchner & van Konijnenburg-van Cittert, 1994; Schweitzer & Kirchner, 1995).
I express my sincere thanks to Mr. Stefan Schmeissner, Kulmbach, and Mr. Günter Dütsch, Untersteinach, for the opportunity to study their collections for comparative material. Dr. M. Kirchner, Munich, is thanked for his stimulating discussions. I am grateful to Eelco Kruidenier for making the photos of the macrofossils and to Niko Korenhof for help with the plates.
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Fig. 1. Male inflorescence; specimen 23116.
Fig. 2. Detail from Figure 1 showing a cluster of eight pollen sacs which yielded in situ pollen.
Fig. 3. Male inflorescence; specimen 10604D.
Fig. 4. Detail from Figure 3, showing several clusters of pollen sacs.
Fig. 1. Part of the content of a pollen sac from specimen 23116, showing monocolpate, granulate pollen grains.
Fig. 2. Part of the content of another pollen sac from specimen 23116.
Fig. 3. Some remains of a pollen sac wall (on the left) and a number of monocolpate, granulate pollen grains.
Fig. 4. A few pollen grains, showing clearly the colpus (upper pollen grain) and the granulate wall.