Physiruellia clade

Note: this taxon list is still under construction. It does not yet contain all known Physiruellia clade subgroups.

Introduction

The Physiruellia clade is a large group characterized by plants with dichasial inflorescences that are often profusely branched and long-pedunculate (see photo below). Species in this clade have fruits that are clavate in shape and seeds with hygroscopic trichomes restricted to the margins (vs. the symplesiomorphic state of covering the entire surface... see Euruellia). Fruits generally contain betwen 8 and 14 ovules.

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Inflorescences of Ruellia brevifolia. ©

The group is particularly diverse in tropical and subtropical regions of western South America, and also occurs in tropical Mexico and Central to N. South America. Most species occupy forest understory environments. Floral morphology is diverse in Physiruellia, with several beautiful, red-flowered taxa likely great candidates for the horticultural industry (gardeners and growers take note!). Some are already in cultivation. Unlike other clades in Ruellia (see Euruellia), purple-flowered taxa are in the minority.

Polylychnis is a monotypic genus endemic to the Guiana Shield. Results from Tripp (in press) place the genus as highly nested within Ruellia. Morphologically, it is very similar to Ruellia, and indeed shares a similar pollen sculpturing. It differs perhaps only by having small projections on the nectary that surrounds the ovary base. However, Ruellia ovaries have never been systematically surveyed to an extent that permits a thorough examination of this potential difference. Based on molecular data and morphological similarity, the new combination Ruellia fulgens (Bremek.) E. Tripp was recently made.

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Flowers of Ruellia fulgens (Bremek.) E. Tripp (= Polylychnis fulgens Bremek.) © 1999 Carol Gracie

Flowers of Ruellia fulgens are long-tubed and red, and are visited by hummingbirds (Gracie 1991). During anthesis, copious, dilute nectar is secreted from the annular ovary disc (11-24 % sugar concentration, >10 µL). After corollas fall, these discs continue secreting nectar, to which ants are attracted and which they consume. However, post-floral nectar is substantially higher in sugar content, ranging from 41-51 %. These ants may serve to guard and protect young, developing fruits.

References

Ezcurra, C. Systematics of Ruellia (Acanthaceae) in southern South America. Annals of the Missouri Botanical Garden 80:787-845.

Gracie, C. 1991. Observation of dual function of nectaries in Ruellia radicans (Nees) Lindau (Acanthaceae). Bull. Torr. Bot. Club. 188(2): 188-190.

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