• Premise of the study: Numerous long‐term studies in seasonal habitats have tracked interannual variation in first flowering date (FFD) in relation to climate, documenting the effect of warming on the FFD of many species. Despite these efforts, long‐term phenological observations are still lacking for many species. If we could forecast responses based on taxonomic affinity, however, then we could leverage existing data to predict the climate‐related phenological shifts of many taxa not yet studied.• Methods: We examined phenological time series of 1226 species occurrences (1031 unique species in 119 families) across seven sites in North America and England to determine whether family membership (or family mean FFD) predicts the sensitivity of FFD to standardized interannual changes in temperature and precipitation during seasonal periods before flowering and whether families differ significantly in the direction of their phenological shifts.• Key results: Patterns observed among species within and across sites are mirrored among family means across sites; early‐flowering families advance their FFD in response to warming more than late‐flowering families. By contrast, we found no consistent relationships among taxa between mean FFD and sensitivity to precipitation as measured here.• Conclusions: Family membership can be used to identify taxa of high and low sensitivity to temperature within the seasonal, temperate zone plant communities analyzed here. The high sensitivity of early‐flowering families (and the absence of early‐flowering families not sensitive to temperature) may reflect plasticity in flowering time, which may be adaptive in environments where early‐season conditions are highly variable among years.

The relative allocation of resources to male and female functions may vary among flowers within and among individual plants for many reasons. Several theoretical models of sex allocation in plants predict a positive correlation between the resource status of a flower or individual and the proportion of reproductive resources allocated to female function. These models assume that, independent of resource status, a negative correlation exists between male and female investment. Focusing on the allocation of resources within flowers, we tested these theoretical predictions and this assumption using the annual Clarkia unguiculata (Onagraceae). We also sought preliminary evidence for a genetic component to these relationships. From 116 greenhouse‐cultivated plants representing 30 field‐collected maternal families, multiple flowers and fruits per plant were sampled for gamete production, pollen : ovule ratio, seed number, ovule abortion, seed biomass/fruit, mean individual seed mass, and petal area. If sex allocation changes as predicted, then (1) assuming that flowers produced early have access to more resources than those produced later, basal flowers should exhibit a higher absolute and proportional investment in female function than distal flowers and (2) plants of high resource status (large plants) should produce flowers with a higher proportional investment in female function than those of low resource status. Within plants, variation in floral traits conformed to the first prediction. Among plants and families, no significant effects of plant size (dry stem biomass) on intrafloral proportional sex allocation were observed. We detected no evidence for a negative genetic correlation between male and female investment per flower, even when controlling for plant size.

Autogamously self‐fertilizing taxa have evolved from outcrossing progenitors at least 12 times in the annual wildflower genus, Clarkia (Onagraceae). In C. xantiana, individuals of the selfing subspecies (ssp. parviflora) flower at an earlier age, produce successive flowers more rapidly, and produce flowers that complete their development more rapidly than their outcrossing counterparts (ssp. xantiana). Two hypotheses have been proposed to explain the joint evolution of these whole‐plant and individual floral traits. The accelerated life cycle hypothesis proposes that selection favoring a short life cycle in environments with short growing seasons (such as those typically occupied by parviflora) has independently favored genotypes with early reproduction, synchronous flower production, and rapidly developing, self‐fertilizing flowers. The correlated response to selection hypothesis similarly proposes that selection in environments with short growing seasons favors early reproduction, but that rapid floral development and increased selfing evolve as correlated responses to selection due to genetic linkage (or pleiotropy) affecting both whole‐plant and floral development. We conducted a greenhouse experiment using maternal families from two field populations of each subspecies to examine covariation between floral and whole‐plant traits within and among populations to seek support for either of these hypotheses. Our results are consistent with the accelerated life cycle hypothesis but not with the correlated response to selection hypothesis.

Summary: Dioecious species may suffer a reproductive handicap compared to sympatric cosexual (hermaphroditic or monoecious) species of equal abundance simply because populations of dioecious species contain fewer seed‐producing individuals. To compensate for this population‐level disadvantage, natural selection in dioecious populations should favour females that reallocate those reproductive resources, that in cosexual individuals are invested in male function, towards the production of higher quality or more seeds, potentially leading to a higher density of established individuals. We tested for two compensatory fitness advantages (heavier seeds and higher population densities) in dioecious species in the flora of a high‐diversity tropical forest in Western Amazonia. Using a phylogenetically corrected generalized linear modelling approach, we examined the phylogenetic dependence (Pagel's λ) of seed mass, abundance, growth form and wood‐specific gravity for 641 species from Yasuní National Park, Ecuador. Seed mass was highly correlated with phylogeny, but abundance was not. We then used AIC values to test for models (including breeding system) that best explained seed mass and species abundance, using the maximum likelihood values of λ. Contrary to expectations, dioecious species exhibited no advantage with respect to either seed mass or population density; there was no difference in mean seed mass or abundance between dioecious species and their most closely related cosexual species. We compared our results with those from a similar forest in the Tambopata Wildlife Reserve, Peru. There, dioecious shrubs had larger seeds than hermaphroditic shrubs, but (as for Yasuní) there was no difference between breeding systems in seed size among trees. Differences in the composition of species sampled may have contributed to differences in the results between the two sites. We suggest that other individual fitness advantages, such as reduced inbreeding, increased dispersal, superior seed quality (e.g. better defences) or increased seed number contribute to the persistence of dioecious populations at Yasuní. Synthesis. Similarities in the statistical models of seed mass and abundance for plant species in a Western Amazonian rain forest indicate that selective pressures on the seed‐producing individuals are similar, despite variation in sexual system. Therefore, breeding system may play a more limited role in community assembly of tropical forests than was previously considered.