Ruellia s. l.

Introduction

Ruellia is a large genus of ca. 300 species. Mexico and Brazil are centers of diversity, but the genus is common elsewhere throughout the neotropics, Madagascar, and mainland Africa. A few species also occur in southeast Asia, Australia, and temperate regions of North America and South America.

Recent molecular work (E. Tripp, in press) indicates Ruellia is monophyletic, though bootstrap support is weak, and early diverging lineages are poorly resolved. Ruellia s. l. encompasses a small number of related genera: Blechum, Eusiphon, and Polylychnis. Old World species form a basal grade, and New World taxa are monophyletic and nested within this grade. The New World clade is composed of several lineages, three of them quite large in size (Euruellia, Physiruellia, and Ebracteolate), and six somewhat smaller in size (the Ruellia inundata, R. inflata, R. jaliscana, R. humilis, R. harveyana and Blechum clades). Floral morphology is diverse within Ruellia. Putatitve pollination syndromes (e. g. bee, hummingbird, bat, hawkmoth) have evolved multiple times suggesting that pollinators have played an important role in the overall diversification of the genus. Pollen morphology (3-porate, spheroidal, coarsely reticulate) represents perhaps the best-known synapomorphy for the genus. Also, a haploid chromosome count of x = 17 has been found for nearly all Ruellia species (over 50 spp.; Daniel & Chuang 1998).

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Left: SEM of Ruellia petiolaris pollen. Right: SEM of Ruellia norvegigratiosa leaf glands. Images © Erin Tripp.

Species of Ruellia can be found in a wide variety of habitats including understory rainforest, desert, swamp, tropical montane, and temperate grassland environments. Most are herbaceous but some are shrubs, small trees, or lianas. A majority of species of Ruellia produce cleistogamous flowers in addition to open (chasmogamous) flowers. The seeds of Ruellia, like other Ruellieae, are covered by hygroscopic trichomes that become mucilaginous when wet. These traits aid in successful reproduction and dispersal, and may help explain the widespread distribution of the genus. Several species of Ruellia are ornamentals, and others have been noted for their local, medicinal uses (e. g., for the treatment of headaches, dizziness, used to make teas, eye drops, and leaves smoked to induce hallucinations; see Daniel 2004 and Wasshausen 2005).

Many (if not most) species of Ruellia possess sessile, inconspicuous leaf glands. These are generally only visible with a dissecting scope. Despite their commonality, these glands have never been systematically studied. It is also not known whether similar structures occur in other, closely related genera. Published images of these glands can be seen in Ezcurra (1993), Daniel (1990), and McDade & Tripp (in press), as well as in the above photo. Research is needed to determine the taxonomic breadth, morphological diversity, and perhaps functional significance of these glands.

References

Daniel, T. F. & T. I. Chuang. 1993. Chromosome numbers of New World Acanthaceae. Syst. Bot. 18: 283-289.

Daniel, T. F. and T. I. Chuang. 1998. Chromosome number of cultivated Acanthaceae and systematic implications. Pp. 309-330 In: Mathew P., Sivadasan M. (eds.) Diversity and taxonomy of tropical flowering plants. Mentor Books. Calicut, India.

Daniel, T. F. 2004. Acanthaceae of Sonora: Taxonomy and Phytogeography. Proc. Cal. Acad. Sci. 55(4): 690-805.

Ezcurra, C. 1993. Systematics of Ruellia (Acanthaceae) in southern South America. Ann. Mo. Bot. Gard. 80: 787-845.

Grant, W. F. 1955. A cytogenetic study of Acanthaceae of Thailand. Brittonia. 8: 121-149.

McDade, L. A. and E. A. Tripp. Synopsis of Costa Rican Ruellia L. (Acanthaceae): New species, taxonomic concepts, a country record, range extensions, and identification aids to the 22 species known from the country. Brittonia, in press.

Tripp, E. A. Evolutionary relationships within the species-rich genus Ruellia (Acanthaceae). Systematic Botany, in press.

Wasshausen, D. C. 2005. Chapter 5.6 Acanthus: Family Acanthaceae. Pp. 112-114. In: G. A. Krupnick and W. J. Kress (eds.). Plant conservation: A natural history approach. University of Chicago Press, Chicago.