Perennials, 7–54 cm (rhizomatous, often matted). Stems (aerial) erect. Leaves mostly cauline; proximal opposite, distal alternate; sessile; blades lanceolate to linear, margins entire, faces hirsute to villous and glandular-pubescent. Heads discoid, borne singly or in loose, corymbiform arrays. Peduncular bracts: pit-glands, tack-glands, and/or spines 0 at tips. Involucres ± campanulate, 5–10+ mm diam. Phyllaries (modified paleae) (5–)7–16 in 1 series, lanceolate to lance-linear, herbaceous, abaxially hirsute and glandular-pubescent. Receptacles flat, setulose, epaleate (except for bracts constituting “involucres”). Ray florets 0. Disc florets 7–29, bisexual, fertile; corollas yellow, tubes shorter than or about equaling funnelform throats, lobes 5, deltate (anthers yellow to brownish; styles glabrous proximal to branches). Cypselae ± terete (apices not beaked, faces scabrellous); pappi of 9–17 white to mauve or tawny, subulate, ± plumose scales (flattened bristles). x = 8.
Carlquistia resembles another montane, perennial tarweed, Anisocarpus scabridus (2n = 14), and the two taxa were long treated as congeneric, in Raillardella or Raillardiopsis. Molecular phylogenetic evidence for a sister-group relationship between Carlquistia and Madia in the strict sense is consistent with x = 8 in both groups (B. G. Baldwin 1996). Carlquistia is treated as distinct from Madia on the basis of morphologic and ecologic disparity between the two groups.
Carlquistia is closely related to the Hawaiian silversword alliance (Argyroxiphium de Candolle, Dubautia Gaudichaud-Beaupré, and Wilkesia A. Gray); vigorous, largely sterile hybrids have been produced between C. muirii and Dubautia laevigata A. Gray, a large shrub of mesic forests in Kauai (B. G. Baldwin et al. 1991). Vigorous hybrids of low fertility also have been produced between C. muirii and the perennial California tarweeds Anisocarpus scabridus and Kyhosia bolanderi (D. W. Kyhos et al. 1990). Diploid pollen from a hybrid between Carlquistia and Kyhosia was successfully used in a cross with Dubautia scabra (de Candolle) D. D. Keck (G. D. Carr et al. 1996).