Abstract Detail

Paleobotany

Allen, Sarah [1], Stull, Gregory W. [2].

Leaf architecture in extant Cannabaceae with a review of select leaf fossils previously assigned to the family.

Cannabaceae, as currently circumscribed, contain 10 genera and ca. 117 species, with the genus Celtis being the most widespread and speciose. Members of Cannabaceae, which are predominantly trees, are found worldwide outside of the polar regions. The family forms a clade with Ulmaceae, Moraceae, and Urticaceae that previously was recognized as the order Urticales, but is now included within Rosales. Fossils representing multiple plant organs have been attributed to the family (or members now placed within it) from the Cretaceous through the Cenozoic, but many of these have not been scrutinized in light of recent phylogenetic/taxonomic changes. Leaf fossils, in particular, deserve attention, given that patterns of leaf architecture have been poorly characterized across our current understanding of Rosales phylogeny. Here, we review leaf characters of Cannabaceae to determine if fossil taxa previously assigned to the family fall within the suite of characters observed in the modern genera. Most genera of Cannabaceae have simple leaves; however, Cannabis has palmately compound leaves. Lozanella, Humulus, and Cannabis typically have opposite leaves, whereas the other genera have alternate phyllotaxy. All genera in Cannabaceae are unlobed, except the palmately lobed Humulus. Most species are toothed, but some species of Gironniera and Chaetachme are untoothed. Teeth, when present, vary in size and frequency. Primary venation is pinnate (e.g., Aphananthe, Chaetachme, Gironniera) to basal actinodromous (Humulus) to a hybrid condition with a pair of strong basal or suprabasal secondaries. Secondary venation in Cannabaceae ranges from craspedodromous to semicraspedodromous to brochidodromous to festooned brochidodromous. Fossil leaf occurrences currently identified as representatives of Cannabaceae include: Humulus from the Late Cretaceous of the Dakotas, U.S.A. and the late Eocene of Colorado, U.S.A.; Trema from the early Paleocene of Ellesmere Island, Canada and the Oligocene of Japan; Pteroceltis from the early Paleocene and Miocene of China; Aphananthe from the late Paleocene of Alberta, Canada; Celtidophyllum from the Late Cretaceous of Russia, Kazakhstan, and Czech Republic; and Celtis from the Cenozoic of North America, Argentina, Bulgaria, Japan, and Russia. Fossils of Celtis aspera, in particular, provide an interesting case study. This species was described from the Paleocene of multiple sites in North America and Russia and has fruits that match extant Celtis, yet the associated leaves are more closely aligned with extant Aphananthe. These records will be reviewed to determine if the characters of the fossil leaves fit within the scope of leaf architecture in extant Cannabaceae.

1 - Penn State Altoona, 206 Hawthorn, 3000 Ivyside Park, Altoona, PA, 16601, United States
2 - Kunming Institute of Botany, Chinese Academy of Sciences, Germplasm Bank of Wild Species, Kunming, Yunnan Province, China

Keywords:
Paleobotany
leaf architecture
Fossil Leaves
Cannabaceae
Rosales.

Presentation Type: Oral Paper
Session: PAL5, Paleobotany III: Patterns and trends
Location: Virtual/Virtual
Date: Tuesday, July 28th, 2020
Time: 3:30 PM
Number: PAL5003
Abstract ID:553
Candidate for Awards:None