Abstract Detail

Paleobotany

Wang, Tengxiang [1], Huang, Jian [2], Liu, Jia [2], Van Do, Truong [3], Nguyen, Hung Ba [2], Su, Tao [2], Wilf, Peter [4].

Fossil leaves of figs (Ficus L., Moraceae) with in-situ cuticles from the Pliocene of central Vietnam.

The fig tree genus Ficus L. (Moraceae) is highly diverse with ca. 750 species worldwide, of which more than 500 are distributed in the Indo-Australasian region. The figs provide food and shelters for a wide variety of mammals, modify forest structure through strangling, and support remarkably specialized mutualisms with fig wasps. Therefore, many Ficus species are considered keystone species in tropical Asian forests. The reliable fossil record of figs is notably scarce. Hundreds of fossil leaf records of Ficus have been reported since the Cretaceous, mostly in older literature, but they have little credibility today because they were based only on the general similarity of leaf architecture, without rigorous comparisons to modern materials, and none has been reported with in-situ cuticles. Cuticular analysis is a powerful tool to assess the botanical affinity of fossil plants, using characters from epidermal and stomatal morphology. Because Ficus shares leaf architecture features with many other genera, including in other families, cuticular analysis is necessary to strengthen the generic and possibly infrageneric identification of potential Ficus leaves. Recently, our international team discovered, reported here for the first time, a new Pliocene flora from a clay-lens deposit in the Kon Tum Formation in Kon Tum Province, Central Highlands region of Vietnam. The assemblage of 572 leaf fossils with cuticular preservation and more than 40 morphotypes comprises the first Cenozoic macroflora reported from southern Indochina. The Pliocene age is preliminarily supported by a rich palynoflora from the same rocks with more than 200 palynotaxa. Nearly all the species in the macroflora have relatively small (mesophyll-microphyll) leaves and are entire margined, consistent with a tropical monsoonal climate, as is the floral composition from preliminary observations. From this flora, more than 40 specimens of Ficus fossil leaves are presented here, supported by both leaf architecture and epidermal structures for the first time in the fossil record of the genus. These leaves are characterized by an ovate lamina, a slight drip tip at the apex, 5–7 pairs of brochidodromous and widely spaced secondary veins, acute basal secondaries, regular and obtuse intersecondaries, and opposite percurrent to reticulate tertiaries, and reticulate quaternaries, together corresponding to the leaf architecture typical of Ficus subg. Urostigma. The stomatal complex is cyclocytic and circular in general shape, while the epidermal cells are irregularly pentagonal with some elongate cells closely aligned, features identical to those of living species from Ficus subg. Urostigma subsect. Conosycea. This subsection is mostly hemi-epiphytic, produces aerial root systems, and has a distribution extending from the Malesian region and Indochina to peninsular India and the Sino-Himalayan region. The new fossils represent the first fossil leaves of Ficus described based on both macro-and microscopic characters and the first unequivocal record reported from Southeast Asia, a center of diversity for the genus. The recognition of Ficus as an abundant element in the Kon Tum flora provides an important new record for the genus and shows that it has been integral to the Asian tropical monsoon forest since at least the Pliocene.

1 - The Pennsylvania State University, Department Of Geosciences, 312 Deike Building, State College, PA, 16802, United States
2 - Xishuangbanna Tropical Botanical Garden, Mengla, Yunnan, China
3 - Vietnam National Museum of Nature, Vietnam, Hanoi, Viet nam
4 - Pennsylvania State University, Geosciences, 537 Deike Bldg., University Park, PA, 16802, United States

Keywords:
Ficus
Pliocene
Vietnam
fossil
Moraceae
Stomata
Southeast Asia.

Presentation Type: Oral Paper
Number: PB2001
Abstract ID:535
Candidate for Awards:Isabel Cookson Award