﻿Townsendialemhiensis (Asteraceae, Astereae): A narrowly endemic new species from Idaho, USA

﻿Abstract Townsendialemhiensis (Asteraceae) is described from the Lemhi Valley of east-central Idaho. From a genus with weak intrinsic isolating barriers, T.lemhiensis remains distinct apparently due to apomixis and to its isolation and habitat specialization on spatially limited occurrences of ashy white soils in the Lemhi Valley. Despite similarities to T.spathulata, this new species differs in its persistent pappus, fewer series of phyllaries and sericeous rather than long woolly hairs.


Introduction
Townsendia Hook. includes about 29 recognized species distributed predominantly throughout the Rocky Mountain and Great Basin regions of western North America (Larsen 1927;Beaman 1957;Shultz and Holmgren 1980). Species of Townsendia are generally characterized by showy inflorescences nestled in a dense rosette of leaves or on short stems; and by a pappus of short bristles. Many species also have strong edaphic affinities that delimit their distribution (Lowrey and Knight 1994). Six species of Townsendia are known to occur in Idaho (T. condensata Parry, 1874, T. florifera (Hook.) A.Gray, 1880, T. hookeri Beaman, 1957, T. leptotes (A.Gray) Osterh., 1908, T. montana M.E.Jones, 1895, and T. parryi D.C.Eaton, 1874, yet none of these species approach the combination of characteristics present in T. lemhiensis.

Field methods
Specimens were initially collected during cursory exploration by Curtis Björk on May 20 th , 2012. Curtis Björk further sampled the area in 2013, and two additional populations were found. In 2018, Chris Lee and Jeannette Whitton used localities provided by Curtis Björk to collect additional samples. We also used satellite imagery of nearby areas to identify potential habitat for T. lemhiensis, and these areas were targeted for additional surveying. Several voucher specimens were taken during each site visit, and dried between newspaper and cushioned cardboard in a plant press. Characters were measured directly from herbarium specimens. Herbaria acronyms follow Index Herbariorum (Thiers 2016).

Pollen counts
We removed 2-3 florets from individual plants and placed them in a 200 μL microtube. After adding approximately 20 μL of lactophenol blue stain to each tube, we vortexed tubes for 20-30 seconds to release pollen into suspension. Slides were prepared using the resulting suspension, and viewed under a standard light microscope. This procedure was repeated multiple times on various specimens but yielded no pollen grains, thus no pollen counts or measurements could be completed. We later examined disk florets from individuals of all known populations under a dissecting microscope, and found that stamens were abortive and evidently non-functional; no anthers were observed. 17541°W, on exposed rocky slope (7371 ft), in areas of grey-white substrate, with bunchgrass, and antelope brush.
Townsendia lemhiensis grows on ashy white slopes of eroded rhyolite tuff. These slopes of powdery soils and friable rock are sparsely vegetated, forming edaphic islands of open ground within a more densely vegetated surrounding matrix of sagebrush steppe. Numerous other plants having narrow geographical ranges occupy similar ashy slopes elsewhere in dry interior regions of western North America (Grimes 1984;Reveal and Björk 2004;Brown and Mansfield 2017). The Lemhi Valley is lined on the east and west by alpine ridges, and the valley floor sits at a high elevation, making it cooler than the sagebrush steppes both further south on the adjacent Snake River Plains and further north in the Salmon-Challis Valleys region.
Associated species growing with Townsendia lemhiensis on the ashy slopes include: Phenology. We observed T. lemhiensis in flower in mid-May over three years (2012,2013,2018). At this time, some individuals had some capitula in bud, and others had mature seeds or open flowers. On this basis, we describe flowering as likely occurring throughout May, and seedset through late May or possibly into June. Further studies are needed to document the timing of bud formation, and potential variation in flowering and fruiting phenology. Another early-flowering species, Townsendia hookeri, co-occurs with T. lemhiensis, and has been observed to set buds in fall that open soon after snow melt (Lee and Whitton, personal observation). Given the early flowering of T. lemhiensis and the presence of snow patches persisting in surrounding areas, we suspect fall bud set may also occur in this species. Co-occurring species of Townsendia were found on site in bud (T. parryi) and late-bud (T. leptotes and T. hookeri).

Discussion
Townsendia lemhiensis is most similar in morphology to T. spathulata Nutt., which shares a generally hairy appearance. However, T. lemhiensis is morphologically distinct because its leaves are narrowly oblanceolate with short dense pubescence, instead of the fleshy, spathulate leaves covered in long, tangled hairs in T. spathulata. Also, the cypselae of T. lemhiensis have persistent pappi rather than the rare characteristic (in Townsendia) of deciduous pappi found only in T. spathulata, T. microcephala and T. condensata (Beaman 1957;Dorn 1992). Its capitulum is protected by fewer phyllary series (2-3), rather than 3-4 phyllary series found in T. spathulata.
Townsendia lemhiensis is morphologically distinct from the seven other species of Townsendia known from this region. We include T. spathulata here, because of its similarity to T. lemhiensis, and because it has been documented in the Beaverhead range overlooking the Lemhi Valley, Idaho (>9000 ft) at the border with Montana (Fig. 3). The seven species of Townsendia in Idaho and adjacent Montana can be distinguished using the taxonomic key below. Four of these species tend to occur at higher elevations (T. condensata, T. leptotes, T. spathulata and T. montana), while T. florifera is often at lower elevations than T. lemhiensis, and is associated with basalt. We found T. parryi, T. leptotes and T. hookeri co-occurring with T. lemhiensis, but these species were in bud, while Townsendia lemhiensis was in full flower. The nearby locality of T. spathulata is Although many Townsendia species occupy distinct geographical ranges and possess a multitude of unique character traits, Beaman (1957) describes them as lacking strong (intrinsic) genetic isolating barriers, based on crossing studies in the greenhouse, and on observed patterns of morphological intergradation in nature (Beaman 1954). While interbreeding is sometimes possible in cultivation, and likely occurs in nature, geographic isolation, phenological differences, and habitat differentiation, especially edaphic specialization, contribute to maintaining species boundaries in this genus. The species recognized by Beaman all include sexually reproducing populations, but apomictic populations also occur in a number of Townsendia species (Beaman 1954(Beaman , 1957. Sexual populations are diploid and outcrossing, while known apomicts are triploid or tetraploid (Beaman 1954). Sexual and apomictic forms typically have distinct (sometimes overlapping) distributions, and provide classic examples of geographical parthenogenesis (Bierzychudek 1985). Apomixis also contributes to maintaining species boundaries, because hybridization involving apomicts is not likely. As a result, hybrids will not necessarily be produced, even where multiple Townsendia species co-occur. Although direct genetic or experimental evidence of apomixis is not available for T. lemhiensis, no pollen was detected on florets sampled from our collections, which strongly suggests that these populations are apomictic. As a result, despite the physical proximity of T. lemhiensis to T. hookeri, T. leptotes, and T. parryi, hybridization is unlikely given that in this region, all four species are likely apomicts (Beaman 1957;Thompson and Whitton 2006). We note that while it is uncommon for species in Townsendia to be recognized based solely on apomictic populations, to date, apomicts have generally fit within the boundaries of morphological descriptions of known sexual populations. In this case, T. lemhiensis has no known sexual populations; whether these are undiscovered or extinct, or whether T. lemhiensis is of hybrid origin is not known.
The first author examined the majority of Townsendia specimens from UBC, UAC, SASK, RM, CS, and UNLV from 2008-2014, and the second author examined all Asteraceae at ID in 2002, and did not find any specimens of Townsendia lemhiensis. Additionally, from 2008-2014, the first author undertook targeted searches for all species of Townsendia throughout their range in WA, ID, MT, WY, CO, NV, NM and CA, and no similar populations were encountered.
Despite the second author's searches in apparently suitable habitats throughout the Lemhi Valley and adjacent valleys in Idaho and Montana in the years 1999-2013, only the three reported populations have been located. Thus it appears that T. lemhiensis is a high priority for conservation. All known occurrences of T. lemhiensis are situated on public land administered by the Bureau of Land Management. Hence, the landscape surrounding this species is somewhat protected from threats, but such a small, rare species may still undergo population reduction from factors such as trampling by cattle or recreationists, invasive exotic plant species, or from climate change that could cause higher frequency and severity of drought and excessive heat events.