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.
Highlights
The present study represents a portion of a survey of wood anatomy in tubiflorous families of dicotyledons
The features that characterize Acanthaceae include: vessels with simple perforation plates and lateral-wall pitting of medium-sized alternate bordered pits ; imperforate tracheary elements with simple pits and libriform fibers; libriform fibers septate in most genera; axial parenchyma vasicentric scanty; rays both multiseriate and uniseriate, the former mostly biseriate; multiseriate portions of multiseriate rays with procumbent cells in a few genera, rays otherwise paedomorphic
The entire family Plantaginaceae is rayless or nearly so (Carlquist 1970), but is probably not as close to either Gesneriaceae or Acanthaceae as it is to Scrophulariaceae, a family which has some rayless species in genera such as Hebe
Summary
The present study represents a portion of a survey of wood anatomy in tubiflorous families of dicotyledons. The families Gesneriaceae (Carlquist and Hoekman 1986a), Myoporaceae (Carlquist and Hoekman 1986b) and Plantaginaceae (Carlquist 1970) are instructive in this regard At another extreme with respect to habit is Mendoncia, a genus of tropical lian as, and Thunbergia, which consists of variously woody vines or (T. erecta) shrubs. The remaining Acanthaceae studied here are from areas of relatively heavy rainfall These species are of interest with respect to ecological wood anatomy because dicotyledons with mesomorphic woods have been assumed to be the VOLUME 12, NUMBER 1 norm instead of diverse adaptations to various kinds of humid and moist conditions. No survey of wood anatomy in Acanthaceae other than their account has appeared elsewhere
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