Rainforests have been a source of lineages to open and seasonally dry habitats throughout Angiosperm evolution, especially in the Neotropics. However, the underlying mechanisms that allow such shifts remain poorly understood at large spatial scales. Here, we test whether acaulescence (an underground stem or a very short stem concealed in the ground) has affected the colonization and speciation in Neotropical seasonally dry habitats by cocosoid palms (Cocoseae). Acaulescent species maintain their growth underground, which increases their chances of survival from prolonged seasonal dry season and frequent fires. We use an integrative approach based on trait‐dependent diversification models, phylogenetic comparative methods, and ecological niche models. We found that shifts towards acaulescent growth form were accompanied by evolutionary transitions to seasonally dry habitats. Acaulescent lineages had higher speciation rates than non-acaulescent ones. However, the interaction between acaulescence and seasonally dry habitats had no significant effect on Cocoseae speciation rates. Acaulescent palms are primarily distributed in Neotropical seasonally dry habitats and non-acaulescent palms are concentrated in Amazonian rainforests. Our results suggest that an underground stem, with high carbohydrate and water storage capacity, is a preadaptation by which rainforest lineages were able to colonize and diversify in new fire-prone, increasingly seasonal and drier adaptive zones. The projected global expansion of dry seasonal habitats requires an understanding of how drought-avoidance functional traits evolve and how they are linked to seasonally dry habitats. Our results are, thus, a step forward in determining plant response mechanisms to drier and seasonal conditions.

Cocoseae_Data.xlsx contains metadata for each of the following datasheets: Table_S1: Data on the growth form and habitat type for all Cocoseae species (i.e. n= 334) obtained from Kissling et al. 2019 and Cassia-Silva et al. 2019 datasets, respectively. Table_S2: Key identification of occurrences records downloaded from the Global Biodiversity Information Facility – GBIF (https://www.gbif.org). Table_S3: Species’ occurrence records individually checked. Table S3 contains the number of records of each species (Records) and metrics widely used to assess model accuracy in the Ecological niche modeling procedure: deviance, COR, and true skill statistic (TSS). The area under the receiver operating characteristic curve (AUC) and initial distribution size (iniDist).

Cocoseae_tree_MCC.txt contains the maximum credibility clade (MCC) tree of the Cocoseae palm tribe.

Cocoseae_tree_100.txt contains 50 phylogenetic trees randomly sampled from the posterior distribution of an all-evidence species-level supertree of palms (Faurby et al. 2016/https://doi.org/10.1016/j.ympev.2016.03.002).

sdm_DRYAD.r contains the script used to run the ecological niche models.

HiSSE.r contains the script used to run all 24 models to the Cocoseae phylogeny
that differed on how their parameters were constrained. Two models were BiSSE-like models (i.e. without hidden states), where turnover (τ = l + m) parameters were free to 100 vary, and extinction fraction (ε) or transitions rates (q) were constrained between growth forms states, depending on the model. Four models corresponded to different CID models, which assumed that rate differences are associated with two (CID-2) or four (CID-4) hidden states and extinctions or 105 transitions were constrained between states. The remaining HiSSE models were trait-dependent diversification models with hidden states, different combinations of parameter constraints, and two different types of transition matrices,one restricted (default) and the other allowing all transitions between character states (Beaulieu and O’Meara 2016).

MuHiSSE.r contains the script used to run all nine MuHiSSE (Multistate Speciation and Extinction with hidden traits) models. One of these was a ‘null model’ where no diversification rate variation is caused by character states. One model was a character-dependent diversification without (i.e. MuSSE-like model) a hidden state and the last seven models included two to eight hidden states (MuHiSSE 2-8 models).

Mapas_global_extent.rar contains all maps generated for the Ecological niche modeling procedure.