Trimezia is a genus of flowering plants in the family Iridaceae, order Asparagales, native to the warmer parts of southern Mexico, Central America, South America, Florida, and the West Indies. It is placed in the tribe Trimezieae of the subfamily Iridoideae.
Plants grow from a corm or rhizome and range considerably in height — from about 7 cm in the smallest species (T. pusilla) to roughly 1.6 m in the largest (T. spathata subsp. sincorana). Linear to lanceolate leaves arise from the base of the plant. Most species bear flowers in shades of yellow. Each flower has six tepals arranged in two series: the outer three (sepals) are noticeably larger than the inner three (petals), and both series often carry brown-purple markings at the base. The stamens have free filaments, and the style is divided into three branches, each typically bearing two lobes.
Several species are known by the English names "walking iris," "apostle's iris," or "apostle plant." New plantlets form at the tips of the flower spikes; once flowering is complete, the spike bends to the ground and the plantlet takes root, so the plant appears to "walk." The "apostle" names stem from the mistaken folk belief that plants will not flower until they have grown 12 or more leaves.
The genus was first formally described by William Herbert in 1844, who attributed the name to Salisbury. The limits of Trimezia have been debated for decades. Molecular phylogenetic studies have shown that the traditionally recognized genera of tribe Trimezieae — Trimezia, Neomarica, Pseudotrimezia, Pseudiris, and Deluciris — are not monophyletic as circumscribed by morphology alone. One consequence, adopted by Plants of the World Online as of early 2025, is to merge all five into a broadly defined Trimezia of roughly 80 accepted species.
Etymology
The name Trimezia derives from the Greek words treis (τρεῖς, "three") and meizon (μείζων, "greater"), referring to the outer three tepals, which are markedly larger than the inner three. The name was attributed by William Herbert in 1844 to Richard Anthony Salisbury, though Salisbury had used it without a formal description.
Distribution
Trimezia is native to the warmer parts of southern Mexico, Central America, South America, Florida, and parts of the West Indies. Species typically inhabit damp grasslands throughout this range.
Ecology
Most Trimezia species grow in damp grasslands across tropical and subtropical America. The genus has an unusual dispersal strategy: new plantlets develop at the end of the flower spikes, which arch downward under their weight after flowering, depositing the plantlet where it takes root — allowing colonies to spread progressively through suitable habitat.
Taxonomy Notes
The circumscription of Trimezia has changed substantially. Three genera were recognized before 2008: Trimezia, Neomarica, and Pseudotrimezia. A fourth, Pseudiris, was published in 2008, and a fifth, Deluciris, in 2018. Molecular phylogenetic analyses have shown the traditionally defined genera are not monophyletic; the main clades each contain species from multiple genera. As of February 2025, Plants of the World Online places Deluciris, Neomarica, Pseudiris, and Pseudotrimezia all within Trimezia, bringing the accepted species count to roughly 80. An alternative classification (Lovo et al. 2018) retains the separate genera with revised circumscriptions.
