G. Rocas et al., LEAF ANATOMY PLASTICITY OF ALCHORNEA-TRIPLINERVIA (EUPHORBIACEAE) UNDER DISTINCT LIGHT REGIMES IN A BRAZILIAN MONTANE ATLANTIC RAIN-FOREST, Trees, 11(8), 1997, pp. 469-473
Alchornea triplinervia trees occur in a montane Atlantic rainforest at
the Macae de Cima State Ecological Reserve (Nova Friburgo, RJ, Brazil
). They are found in two adjacent secondary forests at distinct succes
sional stages: a late-secondary (shaded and humid) and an early-second
ary forest (drier, higher light intensities reaching the understory).
Leaf samples collected in these environments were compared in regard t
o various anatomic parameters. Histochemical tests, anatomic measureme
nts and counting indicated no significant variation for the basic leaf
anatomy. Nevertheless, as compared to the late-secondary forest, the
leaves of the early-secondary forest individuals showed an increased b
ulk of sclerenchyma at the main nervation and petiole, gelatinous fibe
rs with hygroscopic walls all along the central vascular system, thick
er cuticle, a higher abaxial stomatal density, abundance of tannin in
the mesophyll, a significantly thicker palisade and spongy parenchyma,
and compactation of the spongy parenchyma. This anatomical variation
indicates an increased xeromorphism of leaves under the drier conditio
ns of the early-secondary forest. Leaf anatomy plasticity may contribu
te to the high ecological plasticity of this widespread neotropical sp
ecies.