Stuck in a bauplan: architectural uniformity underlies growth form diversity in the tropical forest understorey plant genus Thottea

Background Plant growth form diversity stems from a wide range of life history traits, yet vegetative architecture remains relatively understudied.Aims This study investigated the genus Thottea, a small group of understorey plants in tropical forests, to examine how shifts in growth form relate to variations in plant architecture, woodiness and stem biomechanics.Methods We analysed plant architecture, stem biomechanics, and anatomical features for nine Thottea species from lowland tropical forests in Peninsular India. A molecular phylogenetic framework was used to assess shifts in growth form and related traits.Results All Thottea species displayed a uniform architecture defined by (a) mixed axes (i.e. a single meristem determine both trunk and branch), (b) basal reiteration and (c) repetition of elementary modules. Growth form variations arose from distinct combinations of woodiness, below-ground structures and reiteration processes.Conclusion Key traits such as adaptive reiteration and basal reiteration, above-ground woodiness, mechanical reinforcement and plagiotropy are pivotal to the adaptation of species of Thottea to disturbed and shaded understorey habitats. These trait syndromes represent important life history strategies linked to the challenges of understorey life and have evolutionary implications across the genus.