Wood Anatomy of Acanthaceae: A Survey

Abstract

Qualitative and quantitative wood features are reported for 38 species representing 22 genera, including the scandent genera Mendoncia and Thunbergia. Woods of Acanthaceae are characterized by relatively narrow vessels with simple perforation plates and alternate lateral wall pitting, septate libriform fibers, scanty vasicentric axial parenchyma, rays both multiseriate and uniseriate, erect ray cells abundant in rays (some species rayless or near-rayless), numerous small crystals or cystoliths in ray cells in a few genera (first documented reports of both characters in woods of Acanthaceae), and nonstoried structure. This constellation of features is very closely matched by woods of Gesneriaceae, Scrophulariaceae, Pedaliaceae, Martyniaceae, Bignoniaceae, and Myoporaceae (families listed in order ofdecreasing resemblance). Narrowness ofvessels in tropical Acanthaceae appears related to understory ecology. A few species in warm and seasonally dry areas have narrow, short vessel elements numerous per unit transection. Vasicentric tracheids occur in two nonscandent genera in dry areas. Vessel grouping is roughly proportional to dryness of habitat. Thunbergia alata, T. laurifolia, and all collections of Mendoncia have interxylary phloem (first report for Mendoncia). That feature, plus presence of occasional acicular crystals in rays and axial parenchyma and presence of large gelatinous fibers in phloem ally Mendoncia closely with Thunbergia, and Mendonciaceae is not justified for this and other reasons. Species of Thunbergia differ among themselves, and T. erecta and T. holstii resemble shrubby Acanthaceae more than they do Mendoncia in wood features. Thunbergia thus should not be segregated from Acanthaceae.