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| Reconstruction of flowers, leaf, and whole plant of Hymenaea clade in the Mexican amber. (A) Hymenaea mexicana (Poinar and Brown, 2002), scale bar = 5.0 mm. (B) A bifoliate leaf of H. mexicana, scale bar = 5.0 mm. (C) Hymenaea allendis, scale bar = 5.0 mm. (Calvillo-Canadell et al., 2010). (D) Hypothetical Hymenaea clade tree, scale bar=1.0 m. (E) Hymenaeaphyllum mirandae, scale bar=5.0 mm. (F) Details of brochidodromous secondary veins and abundant translucid glands of Hymenaeaphyllum mirandae, scale bar = 2.0 mm. Hernández-Damián, Rubalcava-Knoth & Cevallos-Ferriz, 2024 Drawings by Aldo Domínguez de la Torre. |
Abstract
One of the most important amber deposits with bioinclusion outcrops in Chiapas, southern Mexico, dated ca. 23–15 Ma (early–middle Miocene). Angiosperms (flowering plants) are the most frequently recorded group, with ca. 16 families based principally on fossil flowers and occasional leaves, including members of Leguminosae. This study reports new bifoliolate-compound leaves preserved in Mexican amber, represented by a pair of leaflets marginally attached to a short petiole. Each leaflet is ovate to oblong with an entire margin and has an acuminate apex with a pinnate primary vein. Their characteristics are comparable with bifoliate compound leaves of extant members of Cercidoideae, Caesalpinioideae, and Detarioideae subfamilies. Their asymmetrical base, brochidodromous secondary veins, and abundant translucid glands allow establishment of a new extinct resin-producing member of the Hymenaea clade (Detarieae, Detarioideae), Hymenaeaphyllum mirandae n. gen. n. sp. Hymenaea clade includes Guibourtia, Hymenaea, and Peltogyne, all with similar foliar architecture and other plant characteristics, including reproductive structures. The connection of Hymenaeaphyllum mirandae with extinct members of resin-producing plants recognized previously is uncertain. The discovery of Hymenaeaphyllum mirandae in the Mexican amber suggests that the Boreotropical Flora extended to low latitudes of North America during the Miocene.
Keywords: Amber, bifoliate leaves, Detarieae, Leguminosae, Miocene
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| Hymenaeaphyllum mirandae n. gen. n. sp., IGM-PB 1550, holotype. (A) General view of the bifoliolate leaf. (B) Line drawing of (A), highlighting preserved leaf architecture. Scale bars = 1 cm. |
Family Leguminosae Jussieu
Subfamily Detarioideae Burmeister
Tribe Detarieae de Candolle
Clade Hymenaea (sensu Fougère-Danezan et al., 2010)
Hymenaeaphyllum Hernández-Damián, Rubalcava-Knoth and Cevallos-Ferriz, n. gen.
Etymology: Highlighting the remarkable similarity of a vegetative organ (leaf) to the Hymenaea clade.
Generic diagnosis: Bifoliolate-compound leaves; two petiolulate leaflets, slightly asymmetrical; petiolule bases pulvinulate; leaflets with asymmetrical base with basal insertion asymmetrical; apex acuminate; elliptical to slightly oblong shape; pinnate primary vein, becoming thinner distally; second-order venation simple brochidodromous, forming irregular arches distally; third-order venation is reticulate irregular but sometimes mixed percurrent veins can be found; translucent gland dots are distributed on the surface of the leaflets in a very high density (50.9 per mm2).
Hymenaeaphyllum mirandae Hernández-Damián, Rubalcava-Knoth and Cevallos-Ferriz, n. sp.
Etymology: The epithet recognizes Dr. Faustino Miranda, a pioneer in the study of plants in Mexican amber.
Repository: Colección Nacional de Paleontología, Museo María del Carmen Perrilliat M., Instituto de Geología, Universidad Nacional Autónoma de México (IGM-PB).
Locality: Simojovel de Allende, Chiapas.
Stratigraphy: La Quinta Formation.
Age: Early–middle Miocene.
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| Reconstruction of flowers, leaf, and whole plant of Hymenaea clade in the Mexican amber. (A) Hymenaea mexicana (Poinar and Brown, 2002), scale bar = 5.0 mm. (B) A bifoliate leaf of H. mexicana, scale bar = 5.0 mm. (C) Hymenaea allendis, scale bar = 5.0 mm. (Calvillo-Canadell et al., 2010). (D) Hypothetical Hymenaea clade tree, scale bar=1.0 m. (E) Hymenaeaphyllum mirandae, scale bar=5.0 mm. (F) Details of brochidodromous secondary veins and abundant translucid glands of Hymenaeaphyllum mirandae, scale bar = 2.0 mm. Drawings by Aldo Domínguez de la Torre. |
Conclusions:
Hymenaeaphyllum mirandae n. gen. n. sp. from Mexican amber is evidence of a geological history of Leguminosae in the Neotropical region during the early–middle Miocene. Foliar characteristics such as leaflets with asymmetrical bases, brochidodromous secondary veins, and translucent gland dots support its inclusion into Detarioideae, especially into the Hymenaea clade, whose members are resin-producing trees. However, it is uncertain how this new species relates to the known extant genera of the clade (Hymenaea, Guibourtia, Peltogyne) due to the remarkable similarity of their foliar architecture and lack of further morphological evidence. This new extinct member of Detarioideae supports the extension of the Boreotropical Flora into the low latitude of North America. However, evidence from other groups of plants suggests that the Boreotropical biogeographic route is essential in extending the distribution of tropical plants into low-latitude North America.
Ana L. Hernández-Damián, Marco A. Rubalcava-Knoth and Sergio R.S. Cevallos-Ferriz. 2024. A New extinct Member of the Resin Producer Group of the Mexican Amber: Hymenaeaphyllum mirandae n. gen. n. sp. (Detarioideae-Leguminosae). Palaeoworld. In Press. DOI: 10.1016/j.palwor.2024.04.004