Does the same morphology mean the same physiology? Morphophysiological adjustments of Philodendron hederaceum (Jacq.) Schott, an isomorphic aroid, to ground- canopy transition Andre ´ Mantovani . Carolina Brito . Dulce Mantuano Received: 11 September 2017 / Accepted: 4 April 2018 Ó Brazilian Society of Plant Physiology 2018 Abstract Lianescent aroids grow horizontally while on the ground (shaded, humid habitats), but switch to vertical growth when they reach a host (exposed, desiccant habitats). There are three morphotypes with respect to leaf adjustment to canopy conditions: isomorphic, allomorphic, and heteromorphic. Allo- morphs and heteromorphs exhibit marked leaf mod- ifications (e.g., leaf area) that have a strategic effect on the plant’s carbon balance, since they increase its light foraging capacity in the canopy. Isomorphs do not show external leaf morphology modifications. There- fore, we hypothesized that leaf anatomy and physiol- ogy change instead, allowing their light foraging capacity to improve while they grow towards the canopy. We evaluated leaf area, lamina-specific mass, mesophyll anatomy, venation density and thickness, stomatal density, chlorophyll concentration and fluo- rescence in leaves of the isomorph Philodendron hederaceum, grown to three heights (terrestrial, 1.5 and 3 m). Stomatal density, chlorophyll a content, and electron transport rate were significantly higher in the canopy leaves (60, 54, and 50%, respectively). Thus, P. hederaceum exhibits leaf adjustments that enhance its light foraging capacity. However, these changes are relatively less marked than those exhibited by sym- patric heteromorphs and allomorphs. Although the canopy leaves of P. hederaceum exhibited a limited improvement in light foraging capacity, the species’ construction and maintenance costs are expected to be lower than those of its sympatric heteromorphs and allomorphs. Future studies that consider leaf lifespan will add another perspective for understanding the costs and benefits of these growth habits in aroid vines. Keywords Philodendron hederaceum Á Isomorphy Á Allomorphy Á Aroid vine Á Heteroblasty 1 Introduction Plants that undergo abrupt and significant changes in the structure and development of their organs are classified as heteroblastic (Zotz 2013). Such changes are regulated both genetically and environmentally (Day 1998; Gamage and Jesson 2007), and they occur in lianescent aroids (Mantovani et al. 2017a). Although the mechanisms that trigger and regulate these transformations are not yet fully understood (Steinitz et al. 1992), it is clear that this phenomenon affects the physiology and ecology of heteroblastic plants in an adaptive manner (Zotz et al. 2011). As lianescent aroids grow from the ground to the canopy in tropical forests, characteristic A. Mantovani (&) Á C. Brito Instituto de Pesquisas Jardim Bota ˆnico do Rio de Janeiro, Rua Pacheco Lea ˜o 915, Jardim Bota ˆnico, Rio de Janeiro, RJ CEP 22460-030, Brazil e-mail: andre@jbrj.gov.br D. Mantuano Laborato ´rio de Ecofisiologia Vegetal, Depto Bota ˆnica, UFRJ, Sala A1-118, Rua Prof. Rodolpho Paulo Rocco s/n8, Rio de Janeiro, RJ CEP 21941-617, Brazil 123 Theor. Exp. Plant Physiol. https://doi.org/10.1007/s40626-018-0105-6