Thyrsanthemum Pichon

Pellegrini, M.O.O., Espejo-Serna, A. Recircumscription and synopsis of Thyrsanthemum and Weldenia (Commelinaceae), two narrow endemic genera from Mesoamerica. Kew Bull 76, 269–286 (2021). DOI: https://doi.org/10.1007/s12225-021-09948-1

Type

Tradescantia floribunda M.Martens & Galeotti [≡ Thyrsanthemumfloribundum (M.Martens & Galeotti) Pichon].

Morphology General Habit

Herbs geophytes, perennial, succulent, base definite, terrestrial or rupicolous

Morphology Roots

Roots tuberous, fusiform

Morphology Stem

Underground stem short, succulent, covered by small scales, sheaths open Aerial stem inconspicuous when young, erect, succulent, unbranched, but becoming elongate during flowering season, sometimes remaining inconspicuous

Morphology Leaves

Leaves sessile to subpetiolate; spirally-alternate, initially congested at the apex of the stem forming a rosette, but becoming more or less distributed along the elongated stem during the flowering season; sheaths closed; ptyxis involute; blades caniculate, base symmetrical, amplexicaul to cordate to cuneate, margins repand, rarely flat, ciliate or glabrous, apex acuminate, midvein conspicuous or not, secondary veins conspicuous or not

Morphology Reproductive morphology Inflorescences Synflorescence

Synflorescences terminal in the distal portion of the stem, main florescence with 1 – several coflorescences

Morphology Reproductive morphology Inflorescences

Inflorescences (main florescences) consisting of a pedunculate, many- to few-branched thyrse, with an elongate main axis; inflorescence bract leaf-like; peduncle bracts present or not; supernumerary bracts absent; cincinni bracts bracteose, unequal to each other, persistent or not, not saccate at base, free from each other; cincinni short- to long-pedunculate, free, elongate, alternate, bracteoles present, generally deciduous, triangular to ovate, imbricate, green or pink to mauve to red or lilac to purple

Morphology Reproductive morphology Flowers

Flowers bisexual or functionally staminate (due to the abortion of the gynoecium), actinomorphic to slightly zygomorphic due to the curvature of the style, chasmogamous, scentless, flat; floral buds obovoid; pedicel inconspicuous to short, not gibbous at apex, upright at pre-anthesis, anthesis and post-anthesis, becoming stout and fibrous in fruit; sepals equal, free, membranous, dorsally striate, margin hyaline, apex obtuse to round, persistent in fruit; petals sessile, equal, free, flat; stamens 6, arranged in two series, subequal, outer stamens shorter than inner ones, filaments free, slightly to strongly sigmoid at anthesis, apex flaccid and pointing to the outside of the flower post-anthesis, medially sparsely barbate with moniliform hairs, hairs concolorous to the petals, anthers versatile, rimose, connective inconspicuous, yellow, anther sacs parallel, C-shaped, yellow, pollen yellow in vivo, exine insulate-cerebroid, sulcal membrane coarsely granular-ridged; ovary sessile, subglobose, green, glandular-pubescent, 3-locular, locules equal, locules 2-ovulate, ovules uniseriate, style slightly sigmoid at anthesis and post-anthesis, white to slightly darker than the petals, cylindrical throughout, stigma truncate to capitellate, white or yellow or pink to lilac, pistil c. the same length as or longer than the stamens

Morphology Reproductive morphology Fruits

Capsules broadly ellipsoid to subglobose, thin-walled, light to medium brown when mature, loculicidal, 3-valved, apex rostrate due to persistent style base

Morphology Reproductive morphology Seeds

Seeds exarillate, up to 2 per locule, ellipsoid to reniform, ventrally depressed, cleft towards the embryotega, testa rugose with ridges radiating from the embryotega, hilum C-shaped, embryotegasemilateral, conspicuous, generally covered by sparse cream farinae, with a prominent apicule or not.

Distribution

Endemic to Mexico, more precisely to central and southern Mexican cordilleras (Hunt 1976, 2015b; Espejo-Serna & López-Ferrari 1995; Espejo-Serna 2012). The distribution of the genus covers the Nearctic and Neotropical regions of Mexico, in the provinces of Chihuahuan Desert, Sierra Madre Occidental, Sierra Madre Oriental, Transmexican Volcanic Belt, Sierra Madre del Sur, Balsas Basin, and Veracruzan (Morrone et al. 2017).

Ecology

All species are geophytes, which perennate by clusters of fusiform tubers during the long winter drought where they occur. During a relatively short summer rainfall period, they initially produce acaulescent rosettes, which ultimately develop into erect or sprawling elongate stems, bearing a terminal synflorescence (Hunt 1976, 2015b). The genus seems to be ecologically associated with volcanic soils (i.e., andosoils, vertisoils; pers. obs.), and rarely with calcareous soils (i.e., calcisoils, including gypsum; Hunt 1976, 2015b).