Data from: Contrasting water, dry matter and air contents distinguish orthophylls, sclerophylls and succophylls (leaf succulents)

Differences in leaf texture (hardness, thickness) distinguish orthophylls
(soft leaves), sclerophylls (hard leaves) and (semi)succophylls
(water-storing leaves). Texture is controlled by dry matter, water and air
contents. Our aim was to a) identify the best index of succulence, b)
assess how these three components vary with leaf type, and c) derive
bounds for these properties among the four main leaf-texture classes.
Eight contrasting species from the Namib Desert, South Africa were
assessed for their leaf area (A), thickness (z), dry mass (D), saturated
water content (Q), and relative volume of dry matter, water and air to
derive various indices of leaf texture. Q/A (= QV•z), where QV is
saturated water storage per unit volume of leaf, is an ideal index of
succulence. Specific leaf area (SLA) is more suitable as an index of
hardness (SLA-1 = D/A) but only among non-succulents. Rising leaf specific
gravity among sclero-orthophylls is due to replacement of air by dry
matter but water among succophylls. Collation of 13 worldwide studies
showed that orthophylls can be distinguished by Q/A ≤ 0.45 mg water mm-2
leaf surface from succophylls with ≥ 0.9, such that there is a divergent
relationship among plants regarding their water-storing properties.
Semi-succophylls can be defined as having a Q/A > 0.45 to <
0.9, and sclerophylls can be separated from orthophylls by a SLA ≤ 10 mm2
mg-1 dry mass. The distribution of these leaf texture classes may vary
greatly within, and especially between, local floras.