Diversity and evolution of samara in angiosperm

Abstract

Samara (winged fruit) can be dispersed easily by wind and may be a crucial factor for angiosperm spread and diversification. In a narrow sense, a samara is an indehiscent dry fruit with wing(s) developed from fruit pericarp, while in a broad sense samaras also include all winged fruits with wings developed from both pericarp and perianth or bracts. According to the wing shape and growth patterns of samaras, we divided samaras into six types, i.e. single-winged, lanceolate-winged, rib-winged, sepal-winged, bract-winged, and perigynous samaras. Perigynous samaras can be further classified into two forms, i.e. round-winged and butterfly-winged samaras. Accordingly, the aerodynamic behavior of samaras can be classified into five types, autogyro, rolling autogyro, undulator, helicopter, and tumbler. The rib-winged and round-winged samaras can be found in Laurales, a basal angiosperm, and may represent the primitive type of early samaras. In the derived clades, samaras evolved enlarged but unequal wings and decreased wing loading (the ratio of fruit weight to wing size), which is likely an adaptation to gentle wind and secondary dispersal through water or ground wind. The wings of some samaras (such as sepal-winged and bract-winged samaras) may have multiple functions including wind dispersal, physical defense for the seeds, and adjust seed germination strategy. The pantropical family Malpighiaceae is extraordinarily rich in samara types, which is likely related to its multiple inter-continent dispersal in history, which is known as "Malpighiaceae Route". Therefore, Malpighiaceae can be used as a model system for the studies on samara adaptation and evolution. We identified the following issues that deserve further examination in future studies using both ecological and evo-devo methods: 1) the adaption of different types of samaras in dispersal processes, 2) the molecular and developmental mechanism of sepal-and bract-wings, and 3) the evolution of samara types and their effects on angiosperm diversification.

Molecular phylogeny of Hiptage (Malpighiaceae) reveals a new species from Southwest China

“…The most distinctive trait in the new species is the arcuate anterior lateral wings of the three-winged mericarp (Figs 2J–K, 3D). Winged mericarps are an adaption for wind dispersal of fruits (Tan et al 2018) and the striking diversity of winged mericarps types in Malpighiaceae indicates that this morphology played a role in long-distance dispersals and speciation (Davis et al 2001, 2002; Qian and Ren 2016; Tan et al 2018). Pingpo Town is located at the northern edge of the distribution range of the genus Hiptage .…”

A new species of Hiptage (Malpighiaceae) from Nujiang Gorge, southwest China

“…The three‐winged samara is a diagnostic trait of the genus Hiptage (Chen and Funston , Tan et al ) and is a key factor facilitating the long‐distance dispersal of the genus. Hiptage lushuiensis has the middle wing much larger than in the to two similar species compared, H. benghalensis and H. tianyangensis (Fig.…”

First fossil evidence of Palaeocarya (Engelhardioideae: Juglandaceae) from India and its biogeographical implications

“…On the basis of the wing shape and growth patterns, Tan et al (2018) divided winged fruits into six types: singlewinged, lanceolate-winged, rib-winged, sepal-winged, bract-winged, and perigynous type. Angiosperm families having characteristic winged fruits include Malpighiaceae, Polygalaceae, Fabaceae, Rhamnaceae, Ulmaceae, Oleaceae, Sapindaceae, Juglandaceae, Cannabaceae, etc.…”