Sedum citrinum Zika 2014, sp. nov.
Creators: name: Zika, Peter F.
Publisher: name: Zenodo
Year: 2014
Subjects: Biodiversity
Taxonomy
Plantae
Tracheophyta
Magnoliopsida
Saxifragales
Crassulaceae
Sedum
Sedum citrinum

description: Sedum citrinum Zika, sp. nov. (Figs. 1–2, 3K–L, 4G–H, 5N–O, 6F–H).
Species nostra Sedo obtusato subsp. boreali affinis, a quo differt inflorescentia superne plana, floribus plus saturate flavis necnon antheris luteis.
Type: — UNITED STATES. California: Del Norte County, ridge 1.4 air km north of South Red Mountain, 1050 m, 9 June 2013, P. F. Zika 26185 (holotype: WTU!; isotypes: BH!, CAS!, GH!, MO!, OSC!, RSA!, UC!, US!).
Rhizomatous herbs, rhizomes and stolons 10–260 × 3–6 mm, often branched and terminating in numerous sterile leafy rosettes. Rosette leaves often loosely arranged with visible internodes, less commonly dense, slightly glaucous, at least when young, green, grey-green, orange to red, or purple, narrowly to broadly obovate, less commonly oblanceolate, cuneate, 10–31 × 6–22 mm, apices obtuse or notched. Stem leaves ascending, slightly glaucous, at least when young, and colored like the rosette leaves, 8–16 × 4–12.5 mm, truncate at base, often narrowly obovate, less commonly oblanceolate or obovate, apices usually obtuse, rarely notched. Flowering stems green to reddish, 5–27.5 cm tall, nodding or bent in bud, erect in flower and fruit. Inflorescences 1.5–12 × 2–9 cm, usually a flat-topped or slightly domed cymose panicle with narrow base and broad, flat or rounded summit, the proximal branches elongated and solitary at the nodes, ascending to spreading or recurving at tips. Inflorescence bracts resembling stem leaves, but smaller, 5–7 × 2–3 mm, oblanceolate, tips acute or blunt. Flowers 10–95 per inflorescence, fresh flower diameter 8–14 mm, flowers 5–merous (7–merous), erect, calyx green or reddish distally, slightly glaucous, at least when young, 2.2–4.5 × 2.7–3.9 mm, sepals fused basally 0.7–1.5 mm, free sepal tips 2–4.5 mm long, apex blunt or acute. Fresh petals 6–9 mm long, bright and deep yellow, midvein yellow or orange (especially in bud), apices or bases sometimes reddish, especially with age; fused at base 0.5–1.2 mm. Petal blade v-shaped in cross section, narrow, spreading or divaricate at 90 degrees to floral axis, apex usually apiculate with subterminal mucro 0.15–0.3 mm. Stamens 10, shorter than petals, filaments green or greenish-yellow, aging red, anthers oblong, 1.2–1.6 × 0.6–0.7 mm, yellow when fresh, after dehiscence aging brown to red, orange, or black. Nectaries nearly rectangular to shallowly crescent-shaped and slightly sunken in middle, dull yellow to white, aging red, 0.7–1.0 × 0.3–0.4 mm. Ovaries 4.9–6.5 mm, erect, fused basally 0.5–1.3 mm, maturing into 5 dark brown erect follicles, 5.2–6.5 mm, with erect to slightly curved style remnant forming a narrow beak 1.2–1.8 mm, follicles fused basally 1.7–2.5 mm, containing 12–16 seeds. Seeds mid-brown, lanceolate, shiny, striate, 1.2– 1.5 × 0.4–0.5 mm, including stipe 0.1–0.3 mm.
Paratypes: — UNITED STATES. California: Del Norte County, ridge 1.6 air km NNW of South Red Mountain, 1210 m, 24 June 2012, P. F. Zika 25931 (HSC!, WTU!); same site, 9 June 2013, Zika 26193 (BH!, CAS!, OSC!, WTU!); ridge 1.4 air km N of South Red Mountain, 1050 m, 24 June 2012, Zika 25930 (CHSC!, JEPS!, OSC!, WTU!); gentle serpentine slope, 2.4 air km NW of South Red Mountain, 1235 m, 9 June 2013, Zika 26201 (CAS!, GH!, OSC!, RSA!, WTU!).
Relationships with other taxa: — Sedum citrinum is assigned to sect. Gormania (Denton 1982). The typical corollas of species in sect. Gormania fall into three general categories (Table 1). One is a pink-flowered corolla with elongate, erect, and narrow-tapering petal tips, displayed by Sedum laxum (Britton in Britton & Rose 1903: 29) A. Berger (1930: 451) subsp. laxum, S. laxum subsp. heckneri (M. Peck 1937: 121) R. T. Clausen (1942: 39), and S. laxum subsp. latifolium R. T. Clausen (1942: 38) (Fig. 3A–C). These subspecies have a distinctive flower shape and color, as well as a unique combination of dark red anthers and pink filaments. The corollas age to red or dark red. Although S. moranii R. T. Clausen (1942: 40) of southwestern Oregon has a similar corolla shape, the flowers are glandular and a different color. A second floral morphology consists of ascending to spreadingascending and rather broad petals, usually pale yellow or white, but sometimes fading to pink with age. Examples of these are S. albomarginatum R. T. Clausen (1975: 424), S. laxum subsp. flavidum Denton (1978: 233), S. obtusatum A. Gray (1868: 342) subsp. obtusatum, S. obtusatum subsp. paradisum Denton (1978: 236), and S. oregonense (S. Watson 1882: 373) M. Peck (1941: 361) (Fig. 3D–J). Strikingly different in the field is a third floral morphology, displayed only by S. obtusatum subsp. boreale R. T. Clausen (1942: 32) and S. citrinum. The petals are relatively narrow and wide-spreading, with age they are sometimes slightly reflexed (Fig. 3K–R). The pale yellow petals and red (less commonly orange or yellow) anthers of S. obtusatum subsp. boreale differ from the deep yellow petals and uniformly yellow anthers of S. citrinum.
Another useful character on fresh plants is the type of growth on the vigorous vegetative offsets, although this can require a bit of experience to interpret correctly. Most species, in sunny situations, display condensed vegetative offsets, with inconspicuous distal internodes, crowded and difficult to see between the leaf bases of the terminal rosette. Examples include Sedum laxum subsp. flavidum, S. laxum subsp. heckneri, S. oblanceolatum R. T. Clausen (1975: 404), and S. obtusatum subsp. obtusatum (Fig. 4A–F). However, any species in a protected or shaded location, such as between two sheltering rocks on a talus slope, seems to suffer less water stress and can infrequently produce elongate vegetative shoot tips. None-the-less, in sunny and exposed situations a few members of sect. Gormania characteristically produce numerous vigorous vegetative shoots, with loose foliage and easily visible distal internodes. These are S. citrinum, S. obtusatum subsp. boreale, and S. oregonense (Fig. 4G–N). In the most exposed and xeric localities, even these taxa can produce relatively dense vegetative shoots, but in general most plants of most populations have well-spaced leaves on the shoot tips. Sedum citrinum can be separated from vegetatively similar plants of S. obtusatum subsp. boreale, and S. oregonense by floral characters, as discussed above and illustrated in Fig. 3.
When working with living material, early in the flowering season, the stem leaves can provide useful taxonomic information when distinctive morphologies are present. However, the stem leaf shape can vary, and some shapes are common among different taxa. The stem leaves on blooming shoots seem to serve as water storage for the flowering effort. They tend to shrivel, then drop off as the flowers age, and are seldom present on herbarium specimens. The most distinctive stem leaves in sect. Gormania have decurrent bases, uniquely found on Sedum laxum subsp. laxum (Fig. 5A–B). Two species have oblanceolate and elongate stem leaves, much like their oblanceolate and elongate rosette leaves; these are S. albomarginatum and S. oblanceolatum (Fig. 5C–E). A few taxa have suborbicular stem leaves with clasping bases, most notably including S. laxum subsp. flavidum, S. laxum subsp. heckneri, and some populations of both S. obtusatum subsp. retusum (Rose, in Britton & Rose 1903: 31) R. T. Clausen (1975: 375), and S. oregonense (Fig. 5F–M). The remaining taxa in sect. Gormania tend to have stem leaves longer than wide, and truncate at the base instead of clasping. This includes S. citrinum, S. laxum subsp. latifolium, S. obtusatum subsp. boreale, S. obtusatum subsp. obtusatum, and most plants of both S. obtusatum subsp. retusum and S. oregonense (Fig. 5N–T).
The inflorescences can provide useful characters for distinguishing species. Some taxa in sect. Gormania have cylindrical inflorescences, with the proximal branches suppressed and short. This includes Sedum obtusatum subsp. boreale (Fig. 6A–E), which typically has an inflorescence 1.5–5 cm wide, with up to 54 flowers. In marked contrast, S. citrinum has a flat-topped inflorescence (Fig. 6F–H), with elongated lower branches. The inflorescence of S. citrinum is usually 2–9 cm wide, and can contain up to 95 flowers. Also noteworthy is the uncommon tendency of some plants of S. citrinum to produce more than one fertile shoot from a single rosette, which is less frequently seen in other members of sect. Gormania (Figs. 1, 6G–H). Sedum obtusatum subsp. boreale does not seem to commonly branch at the base of the fertile shoots (Fig. 6I).
In summary, Sedum citrinum is most similar morphologically to S. obtusatum subsp. boreale (Table 1). They both display widely spaced leaves on their sterile shoots (Fig. 4), and elongate, truncate-based stem leaves (Fig. 5). In critical floral features, both exhibit narrow divergent petals not seen in any other taxa in the section Gormania (Fig. 3). The two are separable by inflorescence shape and width (Fig. 6), as well as by the intensity of the yellow pigment of the corolla and anther color variation (Figs. 2–3). Anthesis ends for S. citrinum in late June as it is starting for S. obtusatum subsp. boreale. In addition, S. citrinum is restricted to ultramafic exposures (Fig. 7), while S. obtusatum subsp. boreale is found on a wide variety of bedrock, including volcanics, metamorphics, and utramafics. Finally, the distribution of S. citrinum is restricted to a tiny portion of Del Norte County, discussed below. The distribution of S. obtusatum subsp. boreale is allopatric, and covers a much larger area to the south and east, in Siskiyou and Trinity counties, over a broader range of elevations. When compared to other members of the group, both S. citrinum and S. obtusatum subsp. boreale differ strongly enough in floral characters to be considered separate species. Related taxa, like S. oregonense to the north, and S. obtusatum subsp. obtusatum to the southeast, have quite different corollas and distributions. (Fig. 3, Table 1).
Etymology:—The epithet citrinum reflects the color of the petals, which are a bright lemon yellow. A proposed common name is Blue Creek stonecrop, as all known records are from within this drainage.
Distribution and conservation:—Blue Creek stonecrop is restricted to the ridges between Red Mountain and South Red Mountain, in southern Del Norte County, California, over a linear distance of less than 4 km, and within an area of roughly 4 square km. The slopes are drained by tributaries of Blue Creek, in the lower Klamath River basin, part of the Klamath Ranges subregion of the California Floristic Province (Baldwin et al. 2012). Geologically the substrate is part of the extensive Josephine Peridotite exposures, which extend for 130 km from Josephine County, Oregon south to Humboldt County, California (Evans 1984).
More field work is needed to determine if there are additional colonies in the immediate area. At present fewer than 2000 plants are known, restricted to three populations in a small zone, suggesting some conservation efforts may be appropriate. More than 20 regional endemics, restricted to serpentine, are listed as rare in the Klamath Ranges by Nakamura and Nelson (2001, Table 3b). Using IUCN criteria (2013), S. citrinum would be vulnerable. It faces some risks in its remote stony habitats, including road-widening, road maintenance and off-road vehicles.
Phenology and ecology: — Sedum citrinum flowers have been recorded from 9–24 June. The habitat is characterized by sunny dry thin soils of serpentine (ultramafic) exposures, on talus or scree, in crevices or between boulders, on flats or ground gently sloping east or west, and on adjacent roadcuts, at elevations of 1050–1235 m (Fig. 7). Common or noteworthy associates include: Adiantum aleuticum (Ruprecht 1845: 49) C. A. Paris (1991: 112), Arctostaphylos nevadensis A. Gray (1878: 27), Aspidotis densa (Brackenridge 1854: 120, pl. 13) Lellinger (1968: 141), Berberis aquifolium Pursh (1813: 219, pl. 4), Calochortus tolmiei Hooker & Arnott (1840: 398), Carex serpenticola Zika (et al. 1998: 261), Ceanothus pumilus Greene (1893: 149), Elymus glaucus Buckley (1862: 99), Horkelia sericata S. Watson (1885: 364), Iris thompsonii R.C. Foster (1936: 199), Juniperus communis Linnaeus (1753: 1040), Montia parvifolia (Moc. ex de Candolle 1828: 361) Greene (1891: 181), Phlox diffusa Bentham (1849: 325), Pinus attenuata Lemmon (1892: 65), P. contorta Douglas ex Loudon (1838: 2292, f. 2210, 2211), Pinus monticola Douglas ex D. Don (in Lambert 1832: unnumbered page following Tab. 80), Polystichum imbricans (D.C. Eaton 1878: 188, pl. 25, f. 3) D.H. Wagner (1979: 50), Quercus vaccinifolia Kellogg (1870: 52), Senecio integerrimus Nuttall (1818: 165), Stipa lemmonii (Vasey 1892: 55) Scribner (1901: 3), Viola lobata Bentham (1849: 298) and Whipplea modesta Torrey (1857: 90).
description: Published as part of Zika, Peter F., 2014, A new species of stonecrop (Sedum section Gormania, Crassulaceae) from northern California, pp. 111-121 in Phytotaxa 159 (2) on pages 112-119, DOI: 10.11646/phytotaxa.159.2.5, http://zenodo.org/record/10089327