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365

Last Page

375

Abstract

Wood anatomy of nonarboreal Scrophulariaceae is little studied, yet such information is needed to understand the evolution of woodiness in the family and order. Description and quantification of wood characters of six species (nine taxa) of Penstemon subgenus Saccanthera show that these woods are specialized. Paedomorphic features include the standard declining-to-level curve of vessel element length by age, and (in several samples) a pronounced tendency to raylessness. Variation in ray characteristics is as great within as between species, suggesting that unsampled populational variation in ray characteristics may be present. Cells intermediate between fibers and nonseptate parenchyma are present and complement the biseriate strands of axial parenchyma. Storying of cambia is found in two species. Crystal presence is erratic; when present, crystals are restricted to pith and rays. Interpreting the paedomorphic origin of the woody habit in Penstemon as an example of heterochrony suggests that comparative life-history and resource-allocation studies may provide powerful tools for placing woodiness in an ecological and evolutionary context in this complex genus.

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© 1986 David C. Michener

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