Ricinospora sp.

Heřmanová, Zuzana, Kvaček, Jiří, Dašková, Jiřina & Halamski, Adam T., 2020, Plant reproductive structures and other mesofossils from Coniacian / Santonian of Lower Silesia, Poland, Palaeontologia Electronica (a 61) 23 (3), pp. 1-23 : 4

Ricinospora sp.

Figure 2 A-C

v 1984 b aff. Istisporites inornatus (Miner) Potonié ; Knobloch, p. 172

Description. Trilete megaspore, 400–530 μm in diameter, flattened in lateral direction, protruding Y mark, reaching one-third of proximal side ( Figure 2B, 2C ), body of spore delicately reticulate with low muri, polygonal lumina ca 10 μm. Exoexine reticulate, on the proximal face covered with complex three-dimensional network of exinal strands arising from muri. Sometimes complex spongiose material covers nearly whole megaspore ( Figure 2C ).

Remarks. The studied megaspores were identified by Knobloch (1984) as aff. Istisporites inornatus (Miner) Potonié. The material is mentioned in his review of mid-European Cretaceous megaspores. However, the complex spongiose material is much more characteristic for the genus Ricinospora . The type R. cryptoreticulata Bergad (1978) described from the Maastrichtian of North Dakota, USA, is of similar size, the trilete body is also round and the surface is reticulate, it also shows similar spongiose material on the surface ( Bergad, 1978). Our material differs in the presence of reticulum with larger lumina and more pronounced muri. Ricinospora sp. differs from R. laevigata Li et al. ( Li et al., 1987) : Ricinospora sp. has delicately reticulate body that can be completely covered by spongiose material, while R. laevigata has a smooth body covered with spongiose material only in the apical part. A similar “irregularly lobed substance” in the apical part is mentioned by Dijkstra (1959) in R. pileata (Dijkstra) Singh, 1983 , from the Maastrichtian of Limburg. The studied material is covered by this substance over nearly whole body, except for the distal apex. However, Lupia (2015) found out that megaspores can lose substantial portions of this spongiose structure. A similar structure has been described in spores of Recent Selaginella by Korall and Taylor (2006), particularly in species S. pygmaea and S. gracillima . Unlike these species, two of our fossil specimens have this mass more extended ( Figure 2A, C ).

Range. Late Coniacian or early Santonian age.

Occurrence. Rakowice Małe locality.

Material studied. K 3014-3019; the material is housed in the National Museum Prague.

Division GYMNOSPERMAE ( Lindley, 1830) Prantl, 1874

Class CONIFERAE ( de Jussieu, 1789) Engler, 1892

Order PINALES Gorozhankin, 1904

Family CUPRESSACEAE Gray, 1821

Genus CUNNINGHAMITES Presl in Sternberg, 1838

Type species. Cunninghamites oxycedrus Presl in Sternberg, 1838, p. 203, pl. 48, figs. 3a-c, pl. 49, figs. 1a, b from Late Cretaceous , Cenomanian; Niederschöna, Saxony, Germany .

Remarks. The leaves are dorsiventrally flattened with expanded leaf cushions, and adaxially showing two distinct bands of stomata, characters that indicate the genus Cunninghamites Presl in Sternberg.

Figures

FIGURE 2. Ricinospora sp. (A) and (C) showing that nearly the whole megaspore is covered with spongiose material, (B) spongiose exinal strengthenings is mainly in the proximal part of spore, a fragment of the trilete laesure is visible. Scale bar for all images 0.1 mm. All specimens from Rakowice Małe locality.