Angiosperms, or Flowering Plants, are the most numerous and diverse Plant group today, dominating almost all terestrial environments. The ealiest Angiosperm fossils appear an the Early Cretaceous, around the shores of the Tethys Ocean, with many Angiosperm groups appearing sudenly, in forms apparently not much different to today, making it impossible to tell how these groups are related without molecular data.
Lotuses, Nelumbonaceae, are aquatic Plants, superficially similar to Water Lilies, to which they were once thought to be related. They grow annually from submerged rhizomatous roots, producing large flar leaves with hydrophobic coatings which lie flat upon the water surface. Surprisingly, molecular analysis of Angiosperm relationships has revealed that Lotuses not closely related to Water Lilies, which are related to Magnolias, but instead are members of the Order Proteales (Proteas), most closely related to Plane Trees. This is particularly surprising as all other members of the Proteales are woody shrubs and trees, while Lotuses are aquatic annual herbs lacking any woody tissue.
In a paper published in ths journal Scientific Reports on 2 June 2023, William Vieira Gobo of the Departamento de Paleontologia e Estratigrafa at the Universidade Federal do Rio Grande do Sul, Lutz Kunzmann of the Abteilung Museum für Mineralogie
und Geologie, Roberto Iannuzzi and Thamiris Barbosa dos Santos, also of the Departamento de Paleontologia e Estratigrafa at the Universidade Federal do Rio Grande do Sul, Domingas Maria da Conceição of the Museu dePaleontologia Plácido Cidade Nuvens at the Universidade Regional do Cariri, Daniel Rodrigues do Nascimento and Wellington Ferreira da Silva Filho of the Departamento de Geologia at the Universidade Federal do Ceará, Julien Bachelier and Clément Coifard of the Structural and Functional PlantDiversity Group at the Freie Universität Berlin, describe a new species of Lotus from the Early Cretaceous Crato Formation of Ceará State, Brazil.
The new species is described from pits to the southwest of Nova Olinda in the Araripe
Basin of northeastern Brazil, and now in the collections of the Museum für Naturkunde in Berlin and the Senckenberg Forschungsinstitut und Naturmuseum in Frankfurt am Main. The authors acknowledge that there are currently unresolved issues concerning fossils from the Crato deposits, with the Brizilian government regarding all removal of the fossils from the country as illegal, and asking that collections in other parts of the world return them, but note that the Brazilian members of the team were invited by the German institutions to come and study the material. The Plant is named Notocyamus hydrophobus, where 'Notocyamus' means 'Southern Bean' in Greek, a refernce to the term 'Egyptian Bean' used by Teophrastos of Eresos to refer to Lotus seeds, and 'hydrophobus' refers to the hydrophobic leaves of Lotus Plants.
Notocyamus hydrophobus (holotype, MB. Pb. 2002/1047). (A) Overview of the
whole plant, with roots, rhizome, leaves, and aggregate fruit in organic connection. A black arrow points to the
part of the peduncle used to make the thin sections. (B) Details of higher-order venation. (C)
Close-up of palinactinodromous venation and the marginal lamina attachment. (D) Close-up on the enlarged
receptacle showing two globose fruitlets (presumed nutlets). Scale bars are 1 cm. Gobo et al. (2023).
The holotype specimen is about 30 cm high and about 25 cm wide, and comprises a rhizome with about 30 roots, 13 leaves, and a single fruiting body. Leaves are 60 to 95 cm long and 60 to 100 mm wide, and oval to eliptical in shape. They are attached to petiole stems 120-200 mm long and 5-10 mm wide. The cells of the leaves are discernable, larger on the upper side than on the lower with each cell bearing a single papilla (hair), agian larger above than below.
Notocyamus hydrophobus (paratype, SMF SM.B 16.522). (A) Isolated leaf. (B), (C)
Close-ups of the pattern of venation. Note that abundant structures interpreted as galls occur along the lamina
and petiole (arrows point to some of them). Scale bars are 5 mm. Gobo et al. (2023).
The fruiting body is borne on a peduncle stem 22.5 cm long and 4 mm wide. Notably, this peduncle has in inner pith layer surrounded by xylem (wood), a tissue not seen in any modern Lotus, but present in all other members of the Order Proteales.
Notocyamus hydrophobus (holotype, MB. Pb. 2002/1047). (A)–(B) Transversal
section of the peduncle. (A) Overview displaying homoxylic wood with abundant fbers interspersed with
parenchymatous rays. Te dashed outline shows the rays connecting with primary xylem that form bundles near
the pith. On the periphery, remains of the cambial zone occur in a discontinuous layer that is followed by new
vascular increments. (B) Close-up of region near pith showing the primary xylem bundles and their connection
with the rays. Abbreviations: pi. pith; px, primary xylem; sx, secondary xylem; r, ray; cz, cambial zone; vi, vascular increments; pxb, primary xylem bundles. Scale bars: (A) 1 mm; (B) 250 µm. Gobo et al. (2023).
The xylum tissue comprises an inner layer of 18 (or possibly 19) primary bundles, surrounded by a secondary homoxylic (vesselless) layer. No growth rings are present, and the whole is surrounded by an ounter layer thought to be the remains of the cambium (bark).
Notocyamus hydrophobus (holotype, MB. Pb. 2002/1047). Radial (A)–(G) and
tangential (H) sections of the peduncle. (A) Overview of region adjacent to the pith (to the far right) showing
vessels in the xylem followed by the secondary xylem with ray and fber cells (to the far left). (B) Primary
xylem cells with helical thickenings and fbers of secondary xylem. (C) A vessel element with scalariform-like
pits and simple perforation plates (arrows). (D) Close-up of a fiber showing simple (black arrow) and slit-like
pits (white arrow). (E) Ray cells with slit-like pit apertures. (F) Overview of region near cambial zone (dashed
outline) showing fber and ray cells in the secondary xylem followed by the layer that gives rise to the new
vascular increments. (G) Fusiform and compressed cells from the cambial zone followed by tracheary elements
with scalariform-like pits. (H) Ray cells in between fbers of secondary xylem. Abbreviations: v, vessels; px, primary xylem; r, ray; f, fber; cz, cambial zone; vi, vascular increments. Scale bars: (A), (F) 200 µm; (B), (C), (E), (G) 50 µm; (D) 25 µm; (H) 100 µm. Gobo et al. (2023).
The Crato Formation has not been dated precisely, but is thought to be slightly more than 120 million years old, which, if correct, would make Notocyamus hydrophobus the oldest known member of the Nelumbonaceae. Molecular dating techniques have suggested that the Nelumbonaceae branched from theit closest relatives, the Platanaceae (Plane Trees) between 83 and 123 million years ago. Since dates at the younger end of this range can be ruled out by other, more modern-looking fossil Lotuses it is not unreasonable to assume that the group dates from the earlier part of this bracket, or possibly a little older. Either way, the assumption that Notocyamus hydrophobus is a very early member of the group, still showing some similarities to non-Lotus relatives, is not unreasonable.
Reconstruction of Notocyamus hydrophobus in its likely environment. Rebecca Dart in Gobo et al. (2023).
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