Abronia and Tripterocalyx are sister genera of ~27 species in the family Nyctaginaceae. They are mostly confined to coastal beaches and dunes, desert sands, or weird high mountain areas. I have been growing and doing field work on these plants since 2014 and, with the help of many wonderful collaborators, have learned a lot of ecology and evolution of these fascinating plants.
Sand verbenas are understudied, probably due to the difficulties in growing them. However, the labs of Karen Samis (PEI) and Chris Eckert (Queen's) have done a lot of really cool work with the coastal species & Thomas Kaye's lab and the Applied Ecology Institute have done a very successful sustained restoration effort of a rare coastal taxa. Yet, there is much interesting going on between the plains and the coast!
Below, I briefly detail some interesting aspects of the genera.
Defense against herbivores
The majority of species are sticky and entrap sand, which defends them against most herbivores. Herbivores feeding on sandy Abronia foliage suffer worn mandibles, reduced growth rate, and longer development times; unsurprisingly, when given the choice, they prefer not to feed on sandy foliage. (Read more in LoPresti and Karban 2016, Ecology, and LoPresti et al. 2018 Ecological Entomology.) Our current work on defense focuses on evolution of defensive strategies and trade-offs between physical and chemical defenses.
Conservation
An alarmingly high proportion of the ~27 species are rare, Ruth Wilson, an early Abronia-phile in 1972 presciently noted in a section called "disappearing species" that "Perhaps [Abronia species] will vanish completely from the major portions of their ranges because of housing and industrial projects, recreation facilities, agriculture, or grazing". Three decades later, one species is on the endangered species list, two are confined to one or few scattered populations along single water bodies, and at least six species are state-listed in one or more states. I am working on collecting and maintaining living collections of these rare species to learn more about their ecology and husbandry requirements as well as to generate a stock of seed.
Pollination
Most species of sand verbena are self-incompatible, and thus, are obligate outcrossers. However, degrees of autogamy have evolved several times within the clade. A very interesting paper by Laura Doubleday (Doubleday et al 2013, American Journal of Botany) showed that selfing populations of Abronia umbellata had smaller flowers and reduced volatile emissions compared to outcrossing populations. Micah Freedman (UC-Davis), an accomplished chemist, Caroline Edwards (Oberlin/MSU), Michael Moore (Oberlin), Marjorie Weber (MSU) and I took volatile profiles of most species, and coupled with ongoing phylogenetic and morphological data, we will examine these evolutionary changes across the several evolutionary origins of self-compatibility in the genus.
Dispersal
Sand verbena achenes are wind-dispersed via rolling, however, wings are very variable both within and among species (in fact, one species is heterocarpic - producing winged and nonwinged achenes within an infructescence!!!). Using field collected fruit, I performed laboratory dispersal assays, with the help of a large fan, to get a relative dispersal kernel for each species. I also have quantified dispersal across transects in a couple species and will gather more data to put into an evolutionary context.
If any other labs are interested in growing these plants, I am (very!) happy to provide seeds and cuttings. The more people working on them, the better! Sand verbenas are somewhat tricky to germinate, but not usually that hard to grow. HERE is my protocol, but I'd love any feedback from folks who grow them.
A DRAFT FIELD KEY TO THIS GROUP. PLEASE TRY IT AND SEND ME COMMENTS!
Publications:
LoPresti, EF and R. Karban. (2016) Chewing sandpaper: grit, plant apparency and plant defense in sand-entrapping plants. Ecology. 97: 826-833
LoPresti, EF; Grof-Tisza, P.; Robinson, M.; Godfrey, J. & R. Karban. (2018). Entrapped sand as a plant defence: effects on herbivore performance and preference. Ecological Entomology 43: 154-161
LoPresti, EF; K Toll & MG Weber. Inflorescence architecture constrains production of diaspore morphs with different dispersal potentials; a field study in Abronia pogonantha (submitted)
