Tradescantia L., Species Plantarum 1: 288. 1753, emend. M.Pell.

Pellegrini, Marco O. O., 2017, Morphological phylogeny of Tradescantia L. (Commelinaceae) sheds light on a new infrageneric classification for the genus and novelties on the systematics of subtribe Tradescantiinae, PhytoKeys 89, pp. 11-72: 29-32

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http://dx.doi.org/10.3897/phytokeys.89.20388

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scientific name

Tradescantia L., Species Plantarum 1: 288. 1753, emend. M.Pell.
status

 

2. Tradescantia L., Species Plantarum 1: 288. 1753, emend. M.Pell.  Figs 6 O–TView Figure 6, 7View Figure 7, 8View Figure 8, 9View Figure 9, 10View Figure 10, 11View Figure 11, 12View Figure 12, 13View Figure 13, 14View Figure 14

Type species.

Tradescantia virginiana  L.

Description.

Herbs chamaephytes or geophytes, base definite or indefinite, perennial, frequently succulent, terrestrial, rupicolous or epiphytes. Roots thin and fibrous or thick and tuberous. Rhizomes absent. Stems prostrate with ascending apex or erect, herbaceous to succulent, rarely fibrous, unbranched to branched only at base or little to densely branched, rooting at the basal nodes or at the distal ones when they touch the substrate. Leaves sessile to subpetiolate; distichously or spirally-alternate, evenly distributed along the stem or congested at the apex of the stem; sheaths closed or split open at maturity; ptyxis involute or convolute; blades flat to falcate and/or complicate, base symmetrical or asymmetrical, midvein conspicuous or not, secondary veins conspicuous or not. Synflorescences  terminal or axillary in the distal portion of the stems, sometimes exclusively axillary, composed of a solitary main florescence or a main florescence with 1-several coflorescences. Inflorescences (main florescences) consisting of a pedunculate double-cincinni fused back to back, sometimes the main florescence composed of 3(-5) cincinni fused back to back, rarely reduced to a solitary cincinnus in axillary inflorescences; inflorescence bract hyaline, tubular, inconspicuous; peduncle bracts present or not; supernumerary bracts present or not; cincinni bracts leaf-like, spathaceous, sometimes reduced (bracteose), generally differing from the leaves mostly only in size, similar to unequal to each other, saccate or not, free from each other; cincinni sessile, contracted, bracteoles inconspicuous or expanded, imbricate or completely involving the cincinnus, linear-triangular to triangular or flabellate, hyaline. Flowers bisexual, actinomorphic or slightly zygomorphic due to the unequal sepals and geniculate pedicels, chasmogamous, flat or tubular, when present floral tube infundibuliform to hypocra teriform, rarely campanulate; pedicel gibbous at apex or not, upright or geniculate at anthesis and pre-anthesis, deflexed at post-anthesis; sepals equal or unequal, free to conate, membranous or chartaceous, rarely fleshy, cucullate, dorsally keeled or not, margin hyaline, apex acute, persistent in fruit; petals sessile or clawed, equal, free to conate, blade flat or plicate; stamens 6, arranged in two series, equal or subequal, filaments free from each other, free from the petals or epipetalous, straight or spirally-coiled at anthesis and post-anthesis, bearded or not with moniliform hairs, when present hair basal or medial or apical, sparse to dense, much shorter or as long as the stamens, anthers basifixed, rimose, connective rhomboid or cordate to sagittate to linearly-tapered or quadrangular to rectangular, generally yellow, but also white or orange or red or pink or lilac, anther sacs ellipsoid or round or C-shaped, divergent, generally yellow, sometimes also white or pink or lilac, pollen generally yellow, sometimes white; ovary sessile, subglobose, white, glabrous, 3-locular, locules equal, locules (1-)2-ovulate, ovules uniseriate, style straight at anthesis, straight or spirally-coiled at post-anthesis, variously colored, obconical or cylindrical at base, cylindrical at length, conical or cylindrical to obconical at the apex, stigma punctate or truncate to capitulate or capitate to trilobate, pistil shorter or the same length or longer than stamens. Capsules subglobose to globose, light to medium brown when mature, loculicidal, 3-valved, sometimes apiculate due to persistent style base. Seeds exarillate, 1-2 per locule, reniform to ellipsoid to narrowly trigonal, ventrally flattened, cleft or not towards the embryotega, testa smooth to faintly rugose to rugose or scrobiculate or costate with ridges radiating from the embryotega, hilum linear, embryotega dorsal or semilateral, conspicuous or not, generally covered by a cream farina, with a prominent apicule or not.

Habitat, distribution and ecology.

Neotropical, ranging from southern USA to Argentina, having Mexico and Central America as its diversity center (Fig. 7View Figure 7). Tradescantia  , as evidenced by its wide distribution and morphological variation, grows in a wide range of environments. The main habitat and ecological traits of the genus are discussed below, under each of the five proposed subgenera.

Phylogenetic placement and circumscription.

With the present recircumscription of Tradescantia  , the genus seems to be finally monophyletic and easily morphologically characterized. Based on molecular and combined data, Tradescantia  is sister to the clade composed by Gibasis  + Elasis  , with these three genera being sister to the clade composed by Tripogandra  s.l. and all lineages of the polyphyletic Callisia  (Bergamo 2003; Evans et al. 2003; Wade et al. 2006; Burns et al. 2011; Zuiderveen et al. 2011; Hertweck and Pires 2014; Pellegrini et al. in prep.). This whole clade (see Fig. 4BView Figure 4) is morphologically supported by the presence of an inconspicuous, hyaline and tubular basal bract, and the main florescence reduced to a double-cincinni fused back to back. As stated in this study and thoroughly discussed by Hunt (1975, 1980, 1983, 1986b), the circumscription of Tradescantia  has been the focus of great discussion since its description by Linnaeus (1753). Since the circumscription adopted in the present study does not match any of the previous circumscriptions, I propose an amendment to the description to the genus, to assure taxonomic clarity and aid taxonomists to recognize it.

Growth form and life cycle.

Despite common misconception, almost all species of Tradescantia  are perennial herbs, lacking a true rhizome. In some species of Tradescantia  , some portions of the stems might become non-chlorophyllate due to shading and produce shortened internodes from being underground. Nonetheless, these stems lack cataphylls and the anatomic characterization needed for them to be correctly classified as rhizomes. Thus, the only perennation structures known for the genus are the well-known tuberous roots, characteristic of T. commelinoides  , T.  subg, Mandonia  (Fig. 12AView Figure 12), T. subg. Setcreasea  , and T. subg. Tradescantia  (Fig. 14AView Figure 14). The only truly annual species are restricted to T. subg. Tradescantia  , but this character is not typical of the subgenus as a whole. Species appearing annual lack conspicuously tuberous roots and occur in the northernmost range of the genus in temperate zones, which may not be hardy during harsh and snowy winters.

Key to the subgenera of Tradescantia