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| Arlenea delicata A.M.N. Ribeiro et al., in Ribeiro, Yang, Saraiva, Bantim, Calixto Jr. et de Lima, 2023. Artwork by Júlia d'Oliveira. |
Highlights:
• Arlenea delicata represents a dioecious plant with specimens bearing female reproductive units, with vegetative and reproductive characters that place it in the Ephedraceae family.
• The macro and micromorphology of Arlenea delicata suggest that it developed in places with a water deficit.
• The shape of the enlarged receptacle, as well as the bract type, indicates that Arlenea delicata seeds may have been dispersed by animals.
Abstract
Ephedroid macrofossils have been widely documented in Cretaceous deposits, including numerous from the Lower Cretaceous Yixian Formation of NE China. However, few ephedroid macrofossils have been reported from South America. Herein, we describe a new plant of the family Ephedraceae, Arlenea delicata gen. et sp. nov., from the Lower Cretaceous Crato Formation of the Araripe Basin, Northeast Brazil, based on the vegetative and reproductive structures. It has the typical morphological characteristics of ephedroid plants, including fertile reproductive branches, opposite phyllotaxy, terminal female cones, a sympodial branching system, longitudinally striated internodes, and swollen nodes. Our new finding is unusual in having inner chlamydosperms subtended by two pairs of bracts, reproductive units connected to branches through swollen receptacles and a smooth seed surface. This new ephedroid taxon from the Crato Formation increases our understanding of plant diversity of this group during the Early Cretaceous. Furthermore, the general morphology (fleshy bracts and enlarged receptacles) of this new fossil discovery indicates that seeds of this plant may have been dispersed by animals such as pterosaurs (mainly the Tapejaridae) and birds (Enantiornithes and Ornituromorpha). If true, this would explain the cosmopolitan distribution of Ephedraceae in the Lower Cretaceous.
Keywords: Early Cretaceous, Gnetophytes, Arlenea delicata, Ephedrales, Crato Formation
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| MPSC PL 3863, the holotype of Arlenea delicata gen. et sp. nov. showing the general morphology of the species. Scale bar = 5 cm. |
Systematic palaeontology
Order Ephedrales Dumortier 1829
Family Ephedraceae Dumortier 1829
Fossil Genus Arlenea A.M.N. Ribeiro et al., gen. nov.
Etymology. Genus (new) Arlenea in honor of a professor and botanist at the Universidade Regional do Cariri, Maria Arlene Pessoa da Silva PhD, for his tireless work in the research and protection of the extant flora of Chapada do Araripe.
Generic diagnosis. Reproductive branches fertile, aphyllous, with terminal female cones, sympodial branching system, internodes longitudinally striated, with swollen nodes, from which 2–3 ramifications depart. Opposite branches of phyllotaxis. Solitary and terminal reproductive structures with oblong-oval to ovoid shape and apparently obtuse to cuspidate apex, show swollen receptacle, two pairs of bracts surrounding two ovals inner chlamydosperms, possibly longitudinally striated. Elongated ovoid to oblong-oval seed shape.
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| Life reconstruction of Arlenea delicata gen. et sp. nov. in the Crato lake. Diagram by Júlia d'Oliveira. |
Arlenea delicata A.M.N. Ribeiro et al., sp. nov.
Etymology. The epithet “delicata” reflects the delicate terminal branches that contain terminal reproductive structures.
Diagnosis. As the same for the genus.
Holotype. MPSC PL 3863 (Fig. 2)
Repository. Palaeobotanical collection of the Museu de Paleontologia Plácido Cidade Nuvens (MPPCN), in Santana do Cariri municipality, Ceará, Brazil.
Type locality. Araripe Basin, Northeast Brazil.
Type horizon. Crato Formation, Lower Cretaceous.
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| Reconstruction of Arlenea delicata. A: plant portion displaying the habit, opposite branches phyllotaxis, and the terminal female cones; B: Enlarged reproductive branch showing terminal FRUs and detail of swollen receptacle; C: Detail of the FRU showing the pairs of proximal and distal bracts and two ovals internal chlamydosperms. Scale bar = 2mm. (Abbreviations: r, receptacle; w1, proximal whorl of bracts; w2, distal whorl of bracts; c, chlamydosperms). Artwork by Júlia d'Oliveira. |
Conclusion:
A new ephedroid plant fossil from the Crato Formation, Lower Cretaceous of the Araripe Basin, Brazil is described based on vegetative and reproductive structures. This fossil ephedroid has longitudinally striated branches and branching, reproductive structures terminal to the branches that carry two internal ovoid chlamydosperms subtended by two pairs of bracts. Based on a detailed comparison with fossil and extant ephedroid plants, we assign the present fossils to a new genus and species, Arlenea delicata gen. et sp. nov., and place it within the family Ephedraceae. The occurrence of Arlenea delicata indicates that ephedroids had a wide distribution in Brazil during the Early Cretaceous. The general morphology (e.g., fleshy bracts and receptacles) of this new ephedroid fossil indicate that seeds of this plant were dispersed by animals. This method of seed dispersal would explain the cosmopolitan distribution of Ephedraceae in the Lower Cretaceous.
Alita Maria Neves Ribeiro, Yong Yang, Antônio Álamo Feitosa Saraiva, Renan Alfredo Machado Bantim, João Tavares Calixto Junior and Flaviana Jorge de Lima. 2023. Arlenea delicata gen. et sp. nov., A New ephedroid Plant from the Early Cretaceous Crato Formation, Araripe Basin, Northeast Brazil. Plant Diversity. In Press. DOI: 10.1016/j.pld.2023.06.008
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