Developmental patterns in anatomy are shared among separate evolutionary origins of stem succulent and storage root‐bearing growth habits in Adenia (Passifloraceae)

Abstract

The architecture of flowering plants is astonishingly diverse. To understand evolutionary patterns and processes that account for this diversity, I investigated developmental anatomy of storage roots and stems of 58 species in the genus Adenia (Passifloraceae) using an explicit phylogenetic context. Because expanded storage roots and stem succulence evolved multiple times in Adenia, patterns of transition between succulent and nonsucculent forms were analyzed using a comparative test that accommodates phylogenetic uncertainty. I tested the innervation hypothesis, wherein I expected the evolution of vascular strands to be correlated with evolutionary increases in water storage tissue if evolution of vascular strands facilitates transport through water and starch storage structures. Not only is evolution of vascular strands in stems statistically coupled with evolutionary increases in parenchyma storage tissue, most lineages that evolved expanded storage roots also evolved vascular strands in these roots in parallel to succulent stems. I proposed that vascular strands and closely associated storage parenchyma found in both roots and shoots of Adenia comprise a homologous unit. A switch-like evolutionary mechanism that alters the spatial expression of this unit between roots and shoots can account, in large part, for transitions between markedly different habits such as storage-rooted herbs and succulent-stemmed shrubs.

Dissection of Evolutionary Networks to Assess Their Role in the Evolution of Robustness, Function, and Diversification

“…Phylogenetic analyses of 52 species in the genus Adenia were as described previously (Hearn , ). Sequences from the ITS1, ITS2, and 5.8S locus (from Hearn ) were aligned and analyzed using a Bayesian analysis of phylogeny to generate a sample of 10,000 trees from the posterior distribution.…”

“…Thus, the network becomes the primary object of study, and it is used to test predictions concerning evolutionary structuring of phenotypic traits, much as a phylogeny forms a basis for further comparative tests. I use this approach to study morphological and anatomical coevolution in the morphologically diverse genus Adenia (Passifloraceae; Hearn , , ).…”

A global analysis of parenchyma tissue fractions in secondary xylem of seed plants

“…Also, RAP, with the exclusion of rayless species (Carlquist, ), is typically higher in angiosperm than in conifer wood for both RP (15–20% compared to 4–8%) and AP (≤ 1% to ≥ 30% compared to ≤ 1%), respectively (Koch, ; Spicer, ). The level of RAP also depends on growth forms, with a surprisingly high level occurring in woody succulents and lianas (Hearn, ). RAP abundance might also change with climate, showing a trend for higher RAP fractions in tropical than in temperate species (Baas, ; Wheeler & Baas, ).…”

Unravelling roots of lianas: a case study in Sapindaceae

“…When the anatomy of roots in general is considered, utilizing the meagre information present in the literature, the general patterns found are the following: root wood tends to be diffuse porous, to have wider vessels than those of the stems (the opposite trend seems to be true for the few lianas studied) and to show larger amounts of parenchyma and not so frequent thinwalled, commonly septate, fibres (Lebedenko, 1962;Patel, 1965;Zimmennann and Potter, 1982;Aloni and Zimmermann, 1983;Carlquist, 1996;Ewers et al, 1997;Machado et al, 1997Machado et al, , 2005Machado et al, , 2007McElrone et al, 2004;Psaras and Sofroniou, 2004;Palhares et al, 2007;Pratt et al, 2007;Goulart and Marcati, 2008;Hearn, 2009;Angélico, 2010). Here we chose Sapindaceae as a model since they are very diverse in their stem anatomy and commonly encountered in Neotropical forests.…”