Trichostema dichotomum

Trichostema dichotomum View in CoL L., Sp. Pl. 2:598. 1753 . TYPE: U.S.A. [VIRGINIA]: ex Virginia, Clayton 177 (LECTOTYPE, designated by Lewis 1945: BM, internet image!) . Originally designated as “type,” here corrected to “ lectotype ” in accordance with Article 9.10 of the ICN ( Turland et al.2018). We reject the later lectotypification of LINN specimen 750.1 ( Reveal et al.1987) as superfluous.

Trichostema brachiatum L. Sp. Pl. View in CoL 2:598. 1753. Isanthus brachiatus View in CoL (L.) Britton, Sterns, & Poggenb., Prelim. Cat. 44. 1888. TYPE: AMERICA Septentrionali [locality uncertain but probably from Virginia; see note] (LECTOTYPE, designated by Reveal in Jarvis et al. 2001: [icon] Dillenius, Hort. Eltham. t. 285, f. 369, BRIT, digital photograph!, MA, internet image!). Notes.— Plate 285 in Hortus Elthamensis was based on plants grown in the Eltham Garden of James Sherard from seed procured by Charles DuBois, Treasurer of the East India Company ( Dillenius 1732:381).Given Charles DuBois position and the name given to this plant by Dillenius,the seeds were likely collected in the Virginia colony. Linnaeus’s (1753) minimal description is non-diagnostic and can be interpreted as compatible with a late-in-the-day specimen of T. dichotomum View in CoL . Dillenius’s plant as figured is obviously and unquestionably T. dichotomum View in CoL ( Table2; Figs.17 View FIG & 18 View FIG ).As the flowers of all members of section Trichostema age, the stamens go from being very long and arched (staminibus longissimis) to being tightly curled within the flower as the flower ages (staminibus brevibus inclusis; pers. obs.; Fig.18 View FIG ).

Trichostema pilosum Roth View in CoL , Nov.Pl.Sp.280.1821.Roth did not cite specific specimens but says that his material came from “Dr.Stüve.” TYPE: U.S.A.:[locality uncertain but likely New Jersey] (SYNTYPES, designated by Roth 1821:destroyed; see Turner 2021). Neotypes are in the process of being chosen for this taxon (McClelland in prep.).

Trichostema dichotomum View in CoL L. var. puberulum Fernald& Griscom,Rhodora 39:445.1937. TYPE: U.S. A. FLORIDA. Duval Co.:dry thickets and woodlands, Oct , A. H. Curtiss 1976 (HOLOTYPE: GH, internet image!; ISOTYPES: CM!, FLAS!, MISSA, US!) . Note.— This variety as described represents several taxa under study by the author (McClelland & Weakley, in review); however, the type specimen has been determined to represent T. dichotomum View in CoL sensu stricto as opposed to one of the other taxa ( McClelland 2022).

Sectional Taxonomy in Trichostema

The affinities of T.coeruleum within the genus Trichostema have been uncertain.Sometimes treated in a separate genus Isanthus , the species has more recently been included in Trichostema , and in sect. Orthopodium ( Lewis 1945) . Current morphologic and phylogenetic evidence (see below in Discussion) suggests that the species is discordant in sect. Orthopodium and is best placed in its own monotypic section. Given that this species was originally named in a separate genus, we retain that name at the new rank of section, creating the new combination:

Trichostema Gronov. sect. Isanthus (Michx.) K.S. McClell, comb. et stat. nov. BASIONYM: Isanthus Michx., Fl. Bor.- Amer. (Michaux) View in CoL 2:3. 1803. TYPE: Trichostema coeruleum (Michx.) K.S. McClell., specimen 74:18 ( Uttal 1984) at P, here designated.

Discussion.— Lewis (1945) placed T. coeruleum (as T. brachiatum ) in sect. Orthopodium based largely on its annual life history, strongly nerved leaves, and base chromosome number of n =7. While these three characters do align T. coeruleum with members of sect. Orthopodium , recent morphological and genetic analyses ( Huang et al. 2008; McClelland 2022; McClelland & Weakley in review; Fig. 20 View FIG ) show that this species does not form a clade with the rest of sect. Orthopodium .

There are several morphological, cytological, and genetic differences (apart from the statistical analyses) that distinguish sect. Isanthus from the other sections. The combination of being an herbaceous annual, having actinomorphic calyces, and having a base chromosome number of n =7 sets sect. Isanthus apart from sects. Chromocephalum , Paniculatum, Rhodanthum , and Trichostema . Morphological characteristics that separate sect. Isanthus from sect. Orthopodium are the two lateral nerves arising near the base of the leaf (vs. multiple lateral nerves arising in a pinnate fashion), greatly reduced inflorescence having a maximum of 3 to 5 flowers per axil (vs. regularly having more than five flowers per inflorescence axil), nearly straight stamens emerging directly from the throat of the corolla (vs. arching stamens emerging along the notch in the two most posterior lobes), and nearly actinomorphic corollas with little differentiation between the four posterior and one anterior lobe (vs. zygomorphic corollas with clear differentiation between the four posterior and one anterior lobe). There is also a genetic characteristic that separates sect. Isanthus from sect. Orthopodium , which is the presence of an eleven base-pair insertion in the ITS-1 gene that is absent in sect. Orthopodium but shared among sects. Isanthus , Trichostema, Rhodanthum , and Paniculatum .

In addition to the genetic and morphological evidence presented, the geographic range of this section does not correspond with that of sect. Orthopodium but rather sects. Paniculatum and Trichostema ( Lewis 1945; McClelland 2022). All other sections are genetically and geographically cohesive in addition to being morphologically and cytologically cohesive ( Lewis 1945, 1960; Huang et al. 2008; McClelland 2022), supporting the recognition of Trichostema sect. Isanthus as a distinct taxon.

Description.— Herbaceous annuals to 40 cm tall; Stems hirtellous with short, downwardly curled hairs, pilose with long, spreading eglandular hairs to 1 mm, occasionally with capitate glands. Leaves elliptic to nearly linear, 2–5 × 0.4–1.6 cm, base subcuneate, margins entire, apex acute. Inflorescences loose, 1–3 (–5)-flowered. Calyx actinomorphic, to 4–7.7 mm in fruit, hirtellous with short, downwardly curled hairs, pilose with long, spreading hairs to 1 mm, with capitate glands, lobes distinct, subequal, narrowly deltate to lanceolate, acute, 1.5–2 times longer than tube; corolla ± actinomorphic, blue-lavender to pale pink-lavender, tube straight, 1.6–3.5 mm, shorter than calyx lobes, anterior lobe 1.3–2.1 mm; stamens 2.3–4.2 mm, ± straight. Nutlets 1.9–2.9 mm, alveolate, hirtellous, with capitate glands, ridges prominent. 2 n =14.

Etymology.— The epithet Isanthus is derived from the genus name Isanthus . The roots of the word are derived from isos, Greek for equal, and anthos, Greek for flower, referring to the nearly actinomorphic flowers.