Mapping the Varieties of Eriogonum microtheca (Great Basin wild buckwheat)

Two varieties of Great basin wild buckwheat (Eriogonum microtheca) are common in the Bodie Hills (var. laxiflorum and var. ambiguum), and a third (var. alpinum) is likely present in a few areas. Several other varieties occur throughout the deserts and mountains of western North America. The characters that distinguish these are, aside from flower color, fairly subtle differences in stem and leaf vestiture (hairiness), leaf size, and plant height. Most of the varieties are difficult to identify with certainty from photographs alone, but some have narrow geographic distributions, which reduces the number of possibilities in many areas to just two or three.

Eriogonum microtheca var. ambiguum (left) and var. laxiflorum (right).

I’ve been wanting to understand these taxa better. So, I’ve mapped the documented locations of each, and I share those maps with you below, along with some notes on identification and links to photos.

First, a few notes:

  1. Is the epithet microthecA or microthecUM ? The spelling was was originally published in 1848 as Eriogonum microtheca, but since 1858 microthecum has been in general use. Apparently, this was an error—probably introduced and widely accepted, because it “sounds right” and the usual practice is to have the genus and epithet endings agree in gender (-um is neuter, -a is feminine). Recently, as microtheca became accepted once more, there was a proposal to conserve microthecum, which (unfortunately in my opinion) did not prevail. So, microtheca it is, but in references that have not been recently updated, microthecum is still widely used. Confusion on this important issue will persist for decades to come.
  2. Data sources: The maps are based mostly on specimen location data downloaded (as KML files) from the Consortium of California Herbaria (CCH), served by the CCH2 data portal and the Intermountain Regional Herbarium Network (IRHN). Several maps include additional “research grade” observations downloaded (as CSV files) from iNaturalist. The map for variety microtheca is based mostly on data from the Consortium of Pacific Northwest Herbaria (CPNWH). Caveat: Some collections or observations may be misidentified or have mis-mapped coordinates, so some locations shown on these maps may be incorrect. The geographic ranges suggested by these maps should be considered very approximate.
  3. Also: Descriptive details and common names are mostly from the Flora of North America treatment of Eriogonum microthecum.
  4. Mapping software: The maps were compiled using Quantum GIS (QGIS), a free, open source Geographic Information System that I’m gradually learning to use. The base map is a combination of “Stamen Terrain Background” and “ESRI Terrain” web map services. Additional minor cleanup and formatting was done in Adobe Photoshop and Adobe Illustrator.

Map 1, var. laxiflorum, var. simpsonii , and var. microtheca. These are the three most widespread varieties. Var. laxiflorum (Great Basin wild buckwheat) (photos) is common across the central and northern Great Basin, and the eastern Sierra-Cascade ranges, up to eastern Washington. Var. simpsonii (Simpson’s wild buckwheat) (photos) is common across the central and southern Great Basin to the western Rocky Mountains and Colorado Plateau. These two are very similar, but the leaf margins of var. simpsonii are revolute (turned under) or nearly so; those of var. laxiflorum are not.

Variety microtheca (Slender wild buckwheat) (photos, specimen images) occurs mostly from central Washington to central Idaho. Its flowers are yellow (flowers of var. laxiflorum and var. simpsonii are mostly white), but so are the flowers of var. ambiguum, which also extends into eastern Washington and western Idaho (see Map 2). The flowering stems and inflorescence branches of var. microtheca are usually glabrous (hairless); those of var. ambiguum are tomentose (with densely interwoven, generally matted hairs) to floccose (with tufts of soft woolly hairs, the tufts often deciduous).

Map 1.

Map 2, var. ambiguum and var. schoolcraftii. Variety ambiguum (Yellow-flowered wild buckwheat) (photos) occurs in the eastern Sierra Nevada and western Great Basin from Inyo County to southeastern Oregon. It is similar to and sympatric with var. laxiflorum, except for its yellow perianth. Its range also overlaps with var. microtheca in eastern Oregon; but, as noted above, the flowering stems and inflorescence branches of var. microtheca are usually glabrous, while those of var. ambiguum are tomentose to floccose.

Variety schoolcraftii (Schoolcraft’s wild buckwheat) (photos) has a very narrow distribution southeast of Honey Lake, in Lassen, Washoe, and perhaps also Plumas counties. It’s very similar to var. ambiguum (yellow flowers and tomentose/floccose herbage), but has slightly larger leaves, flowers, and fruits.

In var. ambiguum: leaf blades are mostly ≤ 0.6 cm wide; flowers are mostly < 2.5 mm long; involucres are 2–2.5 mm long; achenes are 1.5–2 mm long.
In var schoolcraftii: leaf blades are 0.5–1.2 cm wide; flowers are mostly 2.5–3 mm long; involucres are 2.5–4 mm long; achenes are 2.5–3 mm long.

Map 2.

Map 3, var. alpinum. Variety alpinum (Sonora Pass wild buckwheat—though based on its distribution I think it should be “Mono” wild buckwheat) (photos) is known mostly from the eastern Sierra Nevada (and the Sweetwaters, Bodie Hills, and Glass Mountain) in Mono County, plus a few nearby locations in Alpine and Tuolumne counties. With white to rose or reddish corollas, it resembles var. laxiflorum (common throughout the same area), but its stature is shorter, leaves are shorter and narrower with revolute margins, and hairs are often whiter than in var. laxiflorum. It seems to favor the crests of glacial moraines, arid hilltops, and high ridge habitats.

Map 3.

Map 4, var. lapidicola, and var. panamintense. Variety panamintense (Panamint wild buckwheat) (photos, specimen images) is probably restricted to the desert ranges of central Inyo County (one collection in the southern Sierra Nevada may be misidentified). Variety lapidicola (Pahute Mesa wild buckwheat) (photos, specimen images) is known from the Inyo Mountains of Inyo county, the Pahute Mesa/Rainier Mesa area of Nye County, and other scattered locations in central and eastern Nevada as far north as Elko County.

These both differ from var. simpsonii and var. laxiflorum in having flowering stems and inflorescence branches generally glabrous; hairs, if present, are generally brownish or reddish rather than whitish. Both have leaf blades elliptic, and the margins not revolute.

Variety panamintense is a shrub 3–6 dm tall, with leaf blades broadly elliptic, 6–18 mm long × 3–8 mm wide, brown-tomentose below, floccose to subglabrous above; involucres 2–2.5 mm, subglabrous or glabrous; flowers 1.5–2(–2.5) mm; and achenes 1.8–2 mm long.

Variety lapidicola is a subshrub 0.5–0.5 dm tall, with leaf blades elliptic, 3–7(–8) mm long × 1–4 mm wide, densely reddish-brown-tomentose below, tomentose to floccose above; involucres 2.5–3.5 mm, floccose to subglabrous; flowers (1.5–)2–3.5 mm; and achenes 2.5–3 mm long.

Map 4.

Map 5, var. arceuthinum and var. phoeniceum. Both of these are rare, known only from a very few locations in eastern Nevada and western Utah. Varieties laxiflorum, simpsonii, and to a lesser extent lapidicola are also prevalent in this region. Variety arceuthinum (Juniper Mountain wild buckwheat) (specimen images) is known from a scant 5 specimens in the Mahogany Mountains of Lincoln County, Nevada and Iron County, Utah. Variety phoeniceum (Scarlet wild buckwheat) (specimen images) is apparently known from only 3 specimens collected in Millard and Beaver counties, Utah.

Both are short, compact subshrubs, under 10 cm tall. Both have very small, narrowly linear leaf blades, 4–8 mm long and ≤ 1.2 mm wide, densely white-tomentose below and sparsely floccose or glabrous and green above, with revolute margins. The differences are subtle: (1) var. arceuthinum is generally 5–7 cm tall with a spreading caudex, while var. phoeniceum is only 2–4 cm tall, generally without a caudex; (2) var. arceuthinum has glabrous involucres, while var. phoeniceum has floccose to subglabrous involucres. With so few specimens available, and the differences so minor, are these really distinct taxa? More fieldwork needed, I think.

Map 5.

Map 6, var. corymbosoides, var. johnstonii, and var. lacus-ursi. These three varieties occur only in the Transverse ranges of southern California. Of the more widespread varieties, only var. simpsonii may also occur in this area. It differs from these three in having flowering stems and inflorescence branches that are generally tomentose to woolly-hairy (vs. generally glabrous in var. corymbosoides, var. johnstonii, and var. lacus-ursi).

Variety lacus-ursi (Bear lake wild buckwheat) (specimen images) consists of subshrubs about 1.5–2 dm tall, with cream-colored flowers 2.0–2.5 mm long. Its leaves are narrowly elliptic, densely white-tomentose below and glabrous or nearly so above, with the margins usually revolute. It is known only from clayey outcrops in Bear Valley in the San Bernardino Mountains.

Variety johnstonii (Johnston’s or San Gabriel Mountains wild buckwheat) (specimen images) consists of decumbent, spreading subshrubs, less than 1.5 dm tall, with white to reddish flowers mostly 3–3.5 mm long. Its leaves are elliptic to obovate, densely whitish-brown-tomentose below and floccose to subglabrous above, with the margins usually not revolute. It occurs in montane conifer woodlands and was initially known only from high elevations in the San Gabriel Mountains, but has since been found in the San Bernardino Mountains as well.

Variety corymbosoides (San Bernardino wild buckwheat) (specimen images) consists of larger, rounded to spreading shrubs, 3–6 dm tall, with white to reddish flowers 2.0–2.5 mm long. As in var. johnstonii, its leaves are elliptic to obovate, densely whitish-brown-tomentose below and floccose to subglabrous above, with the margins usually not revolute. It occurs in chaparral and in oak and conifer woodlands in both the San Bernardino Mountains and San Gabriel Mountains.

Map 6.

Map 7, All varieties, with (very) approximate range boundaries.

As of this writing, there are no observations in iNaturalist for the rarest varieties of Eriogonum microtheca: vars. arceuthinum, phoeniceum, lacus-ursi, corymbosoides, and johnstonii. These present great opportunities for Nevada/Utah and SoCal botanists to document these taxa with photographs from the field!

When photographing these plants, try to capture the following details: 1) stem hairs: abundance, texture, and color; 2) perianth color; 3) leaf blades: hairiness above and below, margins revolute or not, length (measure); 4) plant height (measure).

Map 7.

Copyright © Tim Messick 2022. All rights reserved.

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