Data from: Repeated origin of three-dimensional leaf venation releases constraints on the evolution of succulence in plants

Succulent water storage is a prominent feature among plants adapted to
arid zones, but we know little about how succulence evolves and how it is
integrated into organs already tasked with multiple functions. Increased
volume in succulent leaves, for example, may result in longer transport
distances between veins and the cells that they supply, which in turn
could negatively impact photosynthesis [1, 2, 3 and 4]. We quantified
water storage [5] in a group of 83 closely related species to examine the
evolutionary dynamics of succulence and leaf venation. In most leaves,
vein density decreased with increasing succulence, resulting in
significant increases in the path length of water from veins to
evaporative surfaces. The most succulent leaves, however, had a distinct
three-dimensional (3D) venation pattern, which evolved 11–12 times within
this small lineage, likely via multiple developmental pathways. 3D
venation “resets” internal leaf distances, maintaining moderate vein
density in extremely succulent tissues and suggesting that the evolution
of extreme succulence is constrained by the need to maintain an efficient
leaf hydraulic system. The repeated evolution of 3D venation decouples
leaf water storage from hydraulic path length, facilitating the
evolutionary exploration of novel phenotypic space.