Tradescantia L. subg. Tradescantia

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: 38-39

publication ID

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

persistent identifier

http://treatment.plazi.org/id/F39765C0-1E2B-120D-E554-4B43F816E07B

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PhytoKeys by Pensoft

scientific name

Tradescantia L. subg. Tradescantia
status

 

2.5. Tradescantia L. subg. Tradescantia  Figs 6TView Figure 6, 11View Figure 11, 14View Figure 14

Tradescantia L. sect. Tradescantia  sensu Hunt (1980), pro parte

Tradescantia sect. Tradescantia ser. Virginianae  D.R.Hunt, Kew Bull. 35(2): 440. 1980, Syn. nov. Type species. Tradescantia virginiana  L.

Tradescantia sect. Tradescantia ser. Tuberosae  D.R.Hunt, Kew Bull. 35(2): 441. 1980, Syn. nov. Type species. Tradescantia tuberosa  Greene (≡ T. pinetorum  Greene)

Ephemerum  Mill., Gard. Dict. Abr., ed. 4.: 462. 1754, Syn. nov. Type species. Ephemerum virginianum  (L.) Mill. (≡ Tradescantia virginiana  L.).

Type species.

Tradescantia virginiana  L.

Description.

Herbs geophytes, base definite, perennial, sometimes annual, succulent, terrestrial or rupicolous. Roots thick, tuberous. Stems erect, sometimes prostrate with apex, succulent, unbranched to little branched to branched only at base, rooting at the basal nodes, rarely rooting at the distal ones when they touch the substrate. Leaves sessile; spirally-alternate, evenly distributed along the stem, sometimes congested at the apex of the stems; sheaths closed, commonly splitting open at maturity; blades falcate and/or complicate, base symmetric, midvein conspicuous, adaxially impressed, abaxially prominent, rounded, secondary veins conspicuous. Synflorescences  terminal in the distal portion of the stems, composed of a solitary main florescence. Inflorescences (main florescences) consisting of a pedunculate double-cincinni fused back to back; inflorescence bract hyaline, tubular, inconspicuous; peduncle bracts absent; supernumerary bracts absent; cincinni bracts leaf-like, unequal to each other, saccate or not, conduplicate, free, overlapping each other; bracteoles expanded, imbricate, linear-triangular to triangular, hyaline. Flowers bisexual, actinomorphic, flat; pedicel non-gibbous at apex, straight at anthesis and pre-anthesis, deflexed at post-anthesis; sepals equal, free, membranous, elliptic to broadly elliptic, not dorsally keeled, apex acute; petals sessile, equal, free, blade ovate to broadly ovate or rhomboid to broadly obovoid to obovoid, flat or plicate, base cuneate to obtuse, margin entire, apex acute to obtuse; stamens 6, arranged in two series, equal, filaments free, straight at anthesis and post-anthesis, to medially densely bearded with moniliform hairs, hairs shorter than the stamens, variously colored, anthers with connective quadrangular to rectangular, yellow, anther sacs C-shaped, yellow, pollen yellow; ovary glabrous, locules 2-ovulate, style straight at anthesis and post-anthesis, variously colored, cylindrical at base, ob conical at the apex, stigma capitate to trilobate, pistil the same length as the stamens. Capsules subglobose to globose, light to medium brown when mature, glabrous, loculicidal, 3-valved, sometimes apiculate due to persistent style base. Seeds exarillate, 1-2 per locule, ellipsoid to narrowly trigonal, ventrally flattened, not cleft towards the embryotega, testa scrobiculate to rugose, with ridges radiating from the embryotega, embryotega dorsal, conspicuous, with a prominent apicule.

Habitat, distribution and ecology.

Tradescantia subg. Tradescantia  is restricted to Canada, USA and Mexico, but considerably more diverse in the USA (Fig. 11View Figure 11). Its species generally grow in open grasslands, pine forests or open rocky areas.

Included species.

The subgenus includes ca. 30 species, namely: Tradescantia bracteata  Small ex Britton, T. cirrifera  Mart., T. edwardsiana  Tharp, T. ernestiana  E.S.Anderson & Woodson, T. gigantea  Rose, T. gypsophila  B.L.Turner, T. hirsuticaulis  Small, T. hirsutiflora  Bush, T. humilis  Rose, T. longipes  E.S.Anderson & Woodson, T. monosperma  Brandegee, T. occidentalis  (Britton) Smyth, T. ohiensis  Raf., T. ozarkana  E.S.Anderson & Woodson, T. pedicellata  Celarier, T. pinetorum  Greene, T. reverchonii  Bush, T. roseolens  Small, T. stenophylla  Brandegee, T. subacaulis  Bush, T. subaspera  Ker Gawl., T. subtilis  Matuda (= T. maysillesii  Matuda), T. tharpii  E.S.Anderson & Woodson, T. virginiana  L., and T. wrightii  Rose & Bush. The species native to the United States have been thoroughly revised by Anderson and Woodson Jr. (1935). However, as stated by the authors, the species concentrated in Mexico are still in need of taxonomic revision, and might reveal taxonomic novelties.

Comments.

Tradescantia subg. Tradescantia  can be easily differentiated from the remaining subgenera by its grass-like appearance (Fig. 14 B–D, FView Figure 14), leaf-sheaths split open at maturity (Fig. 14EView Figure 14), linear leaf-blades (Fig. 14 B–D, FView Figure 14), pedicels apically non-gibbous (Fig. 14H, IView Figure 14), filaments densely bearded with moniliform hairs (Fig. 14 J–LView Figure 14), and stigmatic papillae restricted to the margins of the stigma (i.e. leaving the stylar canal evident; Fig. 14NView Figure 14)). As aforementioned, this subgenus contains the biggest flowers of Tradescantia  , being commonly cultivated all around the world. The group’s taxonomy, ontogeny, cytology, reproductive system, and hybridization were heavily studied by Anderson and Diehl (1932), Anderson and Woodson Jr. (1935), Anderson (1936a, 1936b), Anderson and Hubricht (1938), Anderson and Sax (1936), Celarier (1955), Darlington (1929, 1937), Hubricht and Anderson (1941), King (1933), Riley (1937), Sax and Anderson (1933), Sax and Edmonds (1933), Sax and Humphrey (1934), and Showalter (1938). Nonetheless, the group’s taxonomy remains challenging due to the high frequency of hybridization in nature (see references above) and the recent origin of the group, illustrated by the extremely short branches and poorly-resolved internal relationships recovered by Hertweck and Pires (2014).

Hunt (1980) proposed the distinction of T. subg. Tradescantia ser. Virginianae  and T. subg. Tradescantia ser. Tuberosae  , based solely on the degree of thickening of the roots. Nonetheless, T. subg. Tradescantia ser. Virginianae  is recovered as non-monophyletic in the present analysis, due to the two species from T. subg. Tradescantia ser. Tuberosae  sampled as nested within it. All species in Core Tradescantia  (including T. subg. Tradescantia  ) possess somewhat tuberous roots, and the degree of thickening seems to be of little phylogenetic relevance. Thus, I chose not to recognized any sections or series in T. subg. Tradescantia  . Furthermore, due to the relatively small size of Tradescantia  , and reduced number of species in each subgenus, the recognition of sections and series in the present infrageneric classification seems unnecessary.