Siskiyou checkerbloom Sidalcea malvaeflora ssp. patula, copyright Krzysztof Ziarnek, Kenraiz.

Belongs within: Malvaceae.

Sidalcea, the checker mallows, is a genus of herbs and subshrubs found in western North America.

Checker mallows
Published 23 October 2016

Regular readers may have noticed that it’s been a bit quiet around here lately. The last few weeks at chez Christopher have been… hectic. I have been writing posts but not had the time to publish them. So over the next few days, you’ll be seeing a bit of a run of short posts in quick succession. Keep your eyes out.

Flowering spike of Sidalcea nelsoniana, copyright Rhiannon Thomas.

The handsome plant you see above is a representative of Sidalcea, a genus of about thirty species found in the north of Mexico and the western United States. Members of this genus are commonly known as checker mallows (apparently because of the pattern of veins on the petals of some species); in the British gardening trade, they are also known as prairie mallows. As indicated by their vernacular names, Sidalcea species belong to the mallow family Malvaceae, and are hence related to other flowering plants such as cotton or hibiscus. These affinities are also reflected by their genus name, which is a portmanteau of the names of two other genera of Malvaceae, Sida and Althaea. Checker mallows differ from other members of the Malvaceae in having flowers with stamens that separate from the stamineal column in two tiers, an inner and an outer ring.

Most species of checker mallow are herbs; a few may develop into subshrubs. The genus includes both perennial and annual species. Stems of checker mallows are mostly more or less erect though they are often basally reclining or decumbent towards the base;it is not uncommon for decumbent stems to become secondarily rooted into the ground and develop into spreading stolons (or ‘rhizomes’). Flowers of checker mallows are usually various shades of purple; a small number of species have white flowers (or white forms may occur in usually purple species). Many species of this genus are supposed to be difficult to identify: hybridisation is not uncommon, and some species are quite plastic in their own right. Young plants may also have a quite different appearance, including differently shaped leaves, from mature plants.

Sidalcea campestris, photographed by Amy Bartow.

The primary monograph of Sidalcea was published by E. M. F. Roush in 1931. She divided the genus between three subgenera, two of which contained only a single species each with all the remainder placed in her subgenus Eusidalcea (since the publication of Roush’s monograph, a third non-Eusidalcea species has been recognised). These species are all perennials that, among other features, lack the variation in leaf shape with growth seen in Eusidalcea. More recent molecular analyses have supported Roush’s arrangement arangement (Andreasen & Baldwin 2003). However, they have not supported Roush’s division of Eusidalcea into separate sections for the annual and perennial species; instead, it appears that one or the other habit (it is unclear which) has arisen multiple times.

Like other diverse plant genera found in the California region, Sidalcea has attracted a certain degree of research into its evolutionary dynamics. Comparison of evolutionary rates between species has found that, as might be expected, annual lineages evolve faster than perennial ones (Andreasen & Baldwin 2001). Most species within each life-history class appeared to evolve at similar rates to each other, except for three perennial species: the three non-Eusidalcea species referred to above. One of these species, Sidalcea stipularis (the only one not known to Roush in 1931) showed evidence of an unusually high evolutionary rate for a perennial; this species is restricted to a very small population (only a few hundred plants may exist in the wild) and may have been subject to a higher rate of effective genetic drift. In contrast, the other two species have diverged more slowly than expected. One of these species, S. malachroides, is a presumably slow-lived subshrub; the other, S. hickmanii, commonly germinates after fires from seeds that may have remained in the ground for a number of years. In both cases, the overall result is that particular genotypes may persist in the population longer than in species with a more rapid turnover.

Oregon checkerbloom Sidalcea oregana ssp. spicata, copyright Dcrjsr.

Another feature of Sidalcea population dynamics to have attracted interest is the occurrence in several species of gynodioecy, a phenomenon where some individuals of a population have flowers with both male and female organs whereas other individuals have female organs only. The persistence of such an arrangement raises questions: because hermaphroditic individuals have the potential to contribute to more reproductive pairings than female-only individuals, shouldn’t the former end up out-competing the latter and eliminating them from the population? This has lead to the inference that some factor(s) must give the female-only individuals an advantage that allows them to persist. Ashman (1992) found in germination tests of Sidalcea oregana spp. spicata that seeds that came from female-only plants tended to germinate into healthier, more vigorous offspring than those from hermaphrodites. It may be that plants that can only produce seed by outcrossing are less vulnerable to the effects of inbreeding, or perhaps not having to invest energy in making pollen means that the parent can put more energy into producing seeds.

Systematics of Sidalcea

Characters (from Hickman 1993): Annual or perennial, sometimes from long, creeping rhizomes. Stem generally erect or base more or less decumbent. Leaves generally mostly from near stem base; lowest blades generally crenate to shallowly lobed, upper blades generally deeply lobed (gen more or less compound). Inflorescence generally spike- or panicle-like, generally more open in fruit; bracts at pedicel base 2, generally stipule-like; bractlets subtending calyx generally 0(–3). Flower with calyx lobes as long as or longer than tube; petals purple or rose-pink to white; stamen-tube with generally two series of more or less fused filaments near tip; stigmas linear, on inner side of style branches. Fruit segments generally 5–10, indehiscent, generally more or less beaked, walls thin. Single seed per fruit segment.

    |--S. calycosaH93
    |--S. campestris Greene 1885 [incl. S. asplenifolia Greene 1897, S. sylvestris Nels. 1907]H57
    |--S. candida Gray 1849H57
    |    |--S. c. var. candida [incl. S. c. var. tincta Cockerell 1900]H57
    |    `--S. c. var. glabrata Hitchcock 1957H57
    |--S. covillei Greene 1914 [=S. malvaeflora var. covillei Roush 1931]H57
    |--S. cusickii Piper 1916H57
    |    |--S. c. ssp. cusickii [=S. oregana var. cusickii Roush 1931]H57
    |    `--S. c. ssp. purpurea Hitchcock 1957H57
    |--S. diploscyphaH93
    |--S. glaucescens Greene 1885 [incl. S. montana Congdon 1900]H57
    |--S. hartwegiiH93
    |--S. hendersonii Wats. 1888H57
    |--S. hickmanii Greene 1887H57
    |    |--S. h. ssp. hickmaniiH57
    |    |--S. h. ssp. anomala Hitchcock 1957H57
    |    |--S. h. ssp. parishii (Rob.) Hitchcock 1957 (see below for synonymy)H57
    |    `--S. h. ssp. viridis Hitchcock 1957H57
    |--S. hirtipes Hitchcock 1957H57
    |--S. keckiiH93
    |--S. malachroides (H. & A.) Gray 1868 (see below for synonymy)H57
    |--S. malvaeflora (DC.) Gray ex Benth. 1848 (see below for synonymy)H57
    |    |--S. m. ssp. malvaeflora (see below for synonymy)H57
    |    |--S. m. ssp. asprella (Greene) Hitchcock 1957 (see below for synonymy)H57
    |    |--S. m. ssp. californica (Nutt.) Hitchcock 1957 (see below for synonymy)H57
    |    |--S. m. ssp. celata (Jepson) Hitchcock 1957 [=S. malvaeflora var. celata Jepson 1936]H57
    |    |--S. m. ssp. dolosa Hitchcock 1957H57
    |    |--S. m. ssp. elegans (Greene) Hitchcock 1957 [=S. elegnas Greene 1914]H57
    |    |--S. m. ssp. laciniata Hitchcock 1957H57
    |    |    |--S. m. ssp. l. var. laciniataH57
    |    |    `--S. m. ssp. l. var. sancta Hitchcock 1957H57
    |    |--S. m. ssp. nana (Jepson) Hitchcock 1957 [=S. reptans var. nana Jepson 1936]H57
    |    |--S. m. ssp. patula Hitchcock 1957H57
    |    |--S. m. ssp. purpurea Hitchcock 1957 non S. cusickii ssp. purpureaH57
    |    |--S. m. ssp. sparsifolia Hitchcock 1957H57
    |    |    |--S. m. ssp. s. var. sparsifoliaH57
    |    |    |--S. m. ssp. s. var. hirsuta Hitchcock 1957H57
    |    |    |--S. m. ssp. s. var. stellata Hitchcock 1957H57
    |    |    `--S. m. ssp. s. var. uliginosa Hitchcock 1957H57
    |    `--S. m. ssp. virgata (Howell) Hitchcock 1957 [=S. virgata Howell 1897]H57
    |--S. multifida Greene 1914H57
    |--S. nelsoniana Piper 1919H57
    |--S. neomexicana Gray 1849H57
    |    |--S. n. ssp. neomexicanaH57
    |    |--S. n. ssp. crenulata (Nels.) Hitchcock 1957 [=S. crenulata Nels. 1904]H57
    |    |--S. n. ssp. diehlii (Jones) Hitchcock 1957 [=S. neomexicana var. diehlii Jones 1908]H57
    |    `--S. n. ssp. thurberi (Rob.) Hitchcock 1957 (see below for synonymy)H57
    |--S. oregana (Nutt.) Gray 1849 [=Sida oregana Nutt. in T. & G. 1838]H57
    |    |--S. o. ssp. oreganaH57
    |    |    |--S. o. ssp. o. var. oregana [incl. S. nervata Nels. 1904]H57
    |    |    |--S. o. ssp. o. var. calva Hitchcock 1957H57
    |    |    |--S. o. ssp. o. var. maxima (Peck) Hitchcock 1957 [=S. maxima Peck 1941]H57
    |    |    |--S. o. ssp. o. var. nevadensis Hitchcock 1957H57
    |    |    `--S. o. ssp. o. var. procera Hitchcock 1957H57
    |    |--S. o. ssp. eximia (Greene) Hitchcock 1957 [=S. eximia Greene 1914]H57
    |    |--S. o. ssp. hydrophila (Heller) Hitchcock 1957 [=S. hydrophila Heller 1904]H57
    |    |--S. o. ssp. spicata (Regel) Hitchcock 1957 (see below for synonymy)H57
    |    `--S. o. ssp. valida (Greene) Hitchcock 1957 (see below for synonymy)H57
    |--S. pedata Gray 1887 [=S. spicata var. pedata Jepson 1925]H57
    |--S. ranunculacea Greene 1904 (see below for synonymy)H57
    |--S. reptans Greene 1897 [=S. spicata var. reptans Jepson 1925; incl. S. favosa Congdon 1900]H57
    |--S. rhizomataH57 [=S. calycosa ssp. rhizomataH93]
    |--S. robusta Heller ex Roush 1931 [=S. asprella var. robusta Jepson 1936]H57
    |--S. setosa Hitchcock 1957H57
    |    |--S. s. ssp. setosaH57
    |    `--S. s. ssp. querceta Hitchcock 1957H57
    `--S. stipularisH93

Sidalcea hickmanii ssp. parishii (Rob.) Hitchcock 1957 [=S. hickmanii var. parishii Rob. 1897, S. parishii Rob. ex Davids & Moxley 1923]H57

Sidalcea malachroides (H. & A.) Gray 1868 [=Malva malachroides H. & A. 1840, Hesperalcea malachroides Greene 1892; incl. S. vitifolia Gray 1868]H57

Sidalcea malvaeflora (DC.) Gray ex Benth. 1848 [=Sida malvaeflora DC. 1824, Nuttallia malvaeflora F. & T. in F. & M. 1837]H57

Sidalcea malvaeflora ssp. asprella (Greene) Hitchcock 1957 [=S. asprella Greene 1885, S. malvaeflora var. asprella Jepson 1925]H57

Sidalcea malvaeflora ssp. californica (Nutt.) Hitchcock 1957 [=Sida californica Nutt. in T. & G. 1838, Sidalcea californica Gray 1849, Sidalcea malvaeflora var. californica Jepson 1925]H57

Sidalcea malvaeflora (DC.) Gray ex Benth. 1848 ssp. malvaeflora [incl. Sida delphinifolia Nutt. in T. & G. 1838, Sidalcea delphinifolia Greene 1891, Sidalcea humilis Gray 1849, Sidalcea delphinifolia var. humilis Greene 1891, Sidalcea scabra Greene 1897, Sidalcea rostrata Eastwood 1902]H57

Sidalcea neomexicana ssp. thurberi (Rob.) Hitchcock 1957 [=S. parviflora var. thurberi Rob. ex Gray 1897; incl. S. confinis Greene 1914, S. nitrophila Parish 1899, S. parviflora Greene 1893, S. neomexicana var. parviflora Roush 1931]H57

Sidalcea oregana ssp. spicata (Regel) Hitchcock 1957 [=Callirhoe spicata Regel 1852, S. oregana var. spicata Jepson 1936, S. spicata Greeene 1885; incl. S. spicata var. tonsa Peck 1941]H57

Sidalcea oregana ssp. valida (Greene) Hitchcock 1957 [=S. valida Greene 1897, S. spicata var. valida Wiggins in Abrams 1951]H57

Sidalcea ranunculacea Greene 1904 [=S. reptans var. ranunculacea Jepson 1936, S. spicata var. ranunculacea Roush 1931; incl. S. interrupta Greene 1904]H57

*Type species of generic name indicated


Andreasen, K., & B. G. Baldwin. 2001. Unequal evolutionary rates between annual and perennial lineages of checker mallows (Sidalcea, Malvaceae): evidence from 18S–26S rDNA internal and external transcribed spacers. Mol. Biol. Evol. 936–944.

Andreasen, K., & B. G. Baldwin. 2003. Reexamination of relationships, habital evolution, and phylogeography of checker mallows (Sidalcea; Malvaceae) based on molecular phylogenetic data. American Journal of Botany 90 (3): 436–444.

Ashman, T.-L. 1992. The relative importance of inbreeding and maternal sex in determining progeny fitness in Sidalcea oregana ssp. spicata, a gynodioecious plant. Evolution 46 (6): 1862–1874.

[H93] Hickman, J. C. (ed.) 1993. The Jepson Manual: Higher Plants of California. University of California Press: Berkeley (California).

[H57] Hitchcock, C. L. 1957. A study of the perennial species of Sidalcea. Part I. Taxonomy. University of Washington Publications in Biology 18: 3–79.

Roush, E. M. F. 1931. A monograph of the genus Sidalcea. Annals of the Missouri Botanical Garden 18 (2): 117–244.

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