(3125) Proposal to conserve the name <i>Distichlis stricta</i> ( <i>Poaceae</i> ) with a conserved type

(3125) Distichlis stricta (Torr.) Rydb. in Bull. Torrey Bot. Club 32: 602. 6 Dec 1905 (Uniola stricta Torr. in Ann. Lyceum Nat. Hist. New York 1: 155. Sep 1823) [Angiosp.: Gram.], nom. cons. prop. Typus: U.S.A., California, Mono County, south shore of Mono Lake west of Rush Creek, 37.95633°N, 119.05389°W, 29 Jul 2025, Bell & Poston 1924 (RSA barcode RSA0659203; isotypi: COLO, CS, GH, KSC, MO, NA, NY, RM, UC, US, UTC), typ. cons. prop. Distichlis Raf. (in J. Phys. Chim. Hist. Nat. Arts 89: 104. 1819) is a small genus of dioecious (rarely monoecious), halophytic, rhizomatous and/or stoloniferous grasses. Rafinesque cited D. maritima Raf. (l.c.) as the type for the genus, with Uniola spicata L. and U. maritima Michx. (Fl. Bor.-Amer. 1: 71. 1803), nom. illeg., as synonyms. The name U. spicata has priority making the name D. maritima illegitimate (see Art. 52.2 Ex. 1; Turland & al. in Regnum Veg. 162. 2025). Uniola spicata L. (Sp. Pl.: 71. 1753) is the basionym for D. spicata (L.) Greene (in Bull. Calif. Acad. Sci. 2: 415. 1887), and a lectotype was designated by A.S. Hitchcock (in Contr. U. S. Natl. Herb. 12: 121. 1908) based upon a collection by P. Kalm (LINN 89.4 [image!]). The name Distichlis spicata s.l. is broadly accepted and applied to inland and coastal populations in North and South America (Peterson in Contr. U. S. Natl. Herb. 41: 71–72. 2001 [CNWG]; Barkworth in Fl. N. Amer. 25: 25. 2003; Pohl, World Flora Online [WFO, accessed 9 Sep 2025]; Plants of the World Online [POWO, accessed 9 Sep 2025]). However, an alternative name has been applied to inland North American populations. Uniola stricta Torr. was published (in Ann. Lyceum Nat. Hist. New York 1: 155–156. 1823) based upon a collection made by E. James during the Long Expedition of 1820 (holotype NY barcode 431733!) probably from n.e. New Mexico, along Ute Creek (J.E. Harrington, Ph.D. Diss., Colorado State University: 26. 2010). Rydberg made a new combination, Distichlis stricta (Torr.) Rydb. (in Bull. Torrey Bot. Club 32: 602. 1905), and established D. dentata Rydb. (in Bull. Torrey Bot. Club 36: 536. 1909), distinguishing it from D. spicata and D. stricta based upon the dentation of the pistillate palea. The holotype of D. dentata (NY barcode 380694!) and isotype (NY barcode 380695!) are collections of Sandberg & Leiberg 463 from Washington State. The epithet “stricta” has also been used at the rank of variety: Distichlis maritima var. stricta (Torr.) Thurb. (in Watson & al., Bot. California 2: 306. 1880), D. spicata var. stricta (Torr.) Scribn. (in Mem. Torrey Bot. Club 5: 51 1894), and subspecies: D. spicata subsp. stricta (Torr.) Thorne (in Aliso 9: 195. 1978). Additionally, varieties of D. stricta have been published: D. stricta var. dentata (Rydb.) C.L. Hitchc. (Vasc. Pl. Pacif. N.W. 1: 553. 1969), D. stricta var. laxa (Vasey ex Beal) Fassett & L. West ex Munz (Man. S. Calif. Bot.: 52, 597. 1935; based on D. spicata var. laxa Vasey ex Beal, Grasses N. Amer. 2: 519. 1896). All these combinations are treated as synonyms of D. spicata (L.) Greene by WFO and POWO. In regions where the inland taxon occurs (Great Plains, Intermountain West, Great Basin), the name Distichlis stricta appears in state or provincial floras; it is accepted in H.D. Harrington (Man. Pl. Colorado: 61. 1954); Dorn (Man. Vasc. Pl. Wyoming: 739. 1977, Vasc. Pl. Montana: 185. 1984); Moss & Packer (Fl. Alberta, ed. 2: 86. 1983); Weber & Wittmann (Colorado Fl.: E. Slope: 283. 1996); Ackerfield (Fl. Colorado: 630. 2015, ed. 2: 659. 2022). Albert Spear Hitchcock (Man. Grasses U.S.: 177. 1935) accepted D. dentata, D. spicata, and D. stricta; however, in the 2nd edition of this work A. Chase (Man. Grasses U.S., ed. 2: 177. 1951) reduced D. dentata to a synonym of D. stricta, following J. Reeder (in Bull. Torrey Bot. Club 70: 53–57. 1943). Both Distichlis spicata and D. stricta auct. are highly variable morphologically and frequently occur in large, clonal populations that are dominated by one sex. Distichlis spicata s.l. has been broadly circumscribed using a combination of sexually dimorphic floral and habit characters that overlap with characters used to describe D. stricta; hence it is difficult to distinguish the species with the naked eye. Comparisons of the two species use tendencies to separate them: panicles of D. stricta auct. tend to be less congested than those of D. spicata, staminate inflorescences of D. spicata are exserted above blade tips while those of D. stricta usually reach to the blade tips, D. stricta generally has conspicuous tufts of hairs at the collar while D. spicata has sparse to no hairs. As noted by J. Reeder (l.c.), collections labeled D. stricta or D. dentata (also D. spicata, pers. obs. HLB) frequently have material of only pistillate or staminate plants, making it difficult to compare all the characters that have been used to distinguish these species. Recent taxonomic studies, Bell & Columbus (in Syst. Bot. 33: 536–551. 2008) and Peterson & al. (in Taxon 65: 1263–1287. 2016) found D. spicata to be paraphyletic but did not address the issue of D. stricta. Following up on work by S. Reid (M.S. Thesis, Colorado State University, 2001) and J.E. Harrington (l.c.), cytology has established that Distichlis stricta auct. is derived from D. spicata as the result of a chromosome fusion event (D. stricta 2n = 38, D. spicata 2n = 40) and genomic analysis supports the separation of the two species (Poland & al. preprint: https://doi.org/10.21203/rs.3.rs-4844604/v1). Samples used for this research were collected across North America and include plants grown from seed gathered at the south shore of Mono Lake, USDA National Plant Germplasm System Acc. No. W6 48045. This accession is identified as D. spicata (L.) Greene in the USDA GRIN database; however, cytology and genomics identify the taxon as D. stricta auct. There is no evidence that D. stricta auct. occurs outside of North America. Leaf characters (present in staminate and pistillate plants), first noted by N. Fassett (in Rhodora 27: 67–72. 1925), can distinguish between the 2n = 40 Distichlis spicata and the 2n = 38 plants of D. stricta auct. The leaf tips of D. spicata are blunt to prow-shaped with leaf margins irregularly and minutely toothed; those of D. stricta auct. are needle-like with minutely serrate leaf margins. As checked by HLB, the tips of the holotype of U. stricta (NY barcode 431733!) and the holotype (NY barcode 380694!) and isotype (NY barcode 380695!) of D. dentata are blunt and cannot serve as types for D. stricta auct. Andrea Deneau (Linnean Society of London, pers. comm. to HLB, 19 March 2025) kindly provided macro images of leaf tips of LINN 89.4! (lectotype of Uniola spicata L.). These images clearly show the tips to be prow-shaped. Blade tips from Mono, Lassen, and Modoc counties in California and other parts of the distribution of D. stricta auct. are needle-like (HLB, pers. obs.). Rejection of this proposal would maintain the broad circumscription of Distichlis spicata and will not require any changes to nomenclatural (IPNI, WFO, POWO, CNWG), floristic (Fl. N. Amer., SEINet Portal Network, Jepson eFlora), or herbarium databases. Unfortunately, it would also maintain an incorrect understanding of relationships in the grass genus Distichlis. Guidelines provided by Wiersema & McNeill (https://www.iaptglobal.org/_files/ugd/fc7907_2b6ebbc7ac63422798515a18c2b27fe6.pdf 2025) direct that proposals can provide a change of type to “preserve current usage”. Acceptance of this proposal will facilitate application of a correct name that reflects the evolutionary history of Distichlis. By gathering material from a site (Mono Lake) associated with recent studies, we are proposing a conserved type that has morphological, cytological, and genomic characters known to belong to D. stricta, as that name has been widely applied to inland North American populations by many authors. Acceptance of the neglected name, D. stricta, for these populations is a step toward greater understanding of D. spicata s.l. We are grateful to J.H. Wiersema for helpful comments on earlier drafts and for guidance on the preparation of a proposal. Thanks also to Travis Columbus, Vanessa Ashworth, Paul Peterson, and Rob Soreng for their suggestions. Muriel Poston provided valuable support and advice.

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