California

Sidalcea hickmanii E.Greene subsp. hickmanii (MALVACEAE).—San Mateo Co., Santa Cruz Mtns., Butano Ridge, Pescadero Creek County Park (San Mateo County Department of Parks), on southwest-facing flank of ridge, 37.24194, –122.25122, 460 m, 18 March 2022, K. Hickman s.n. (JEPS129874). 100+ fire-germinated plants scattered across sandy soil patches in unusual 8–10-acre area of Eocene-age sandstone, where the only known grove of Hesperocyparis abramsiana (C.B.Wolf) Bartel var. butanoensis (Silba) Bartel & R.P.Adams occurs (Fig. 1A). The site, as described by McMillan (1952) when he collected the cypress in 1951, “is approximately eight to ten acres in area containing as a rough estimate five thousand trees. Some of the larger cypresses are sixty to seventy-five feet in height with the average being possibly twenty to thirty feet. The entire population is visible from a portion of exposed sandstone in the area and was found to be surrounded on all sides by a taller forest composed principally of Sequoia sempervirens (Lamb.) Endl., Pseudotsuga taxifolia (Lamb.) Britt. [Pseudotsuga menziesii (Mirb.) Franco], and Arbutus menziesii Pursh. Within the cypress area, no other trees were found, but of the shrubs, Adenostoma fasciculatum Hook. & Arn. was the most abundant. Sphacele calycina (Benth.) Epling ex Munz [Lepechinia calycina (Benth.) Epling ex Munz], Eriodictyon californicum (Hook. & Arn.) Torr., and Arctostaphylos tomentosa (Pursh) Lindl. [Arctostaphylos crustacea Eastw.] were other common shrubs of the cypress area.” Germination of the Sidalcea hickmanii was triggered by the 2020 CZU Lighting Complex Fire that burned over 86,000 acres in the Santa Cruz Mountains, including Butano Ridge and the entire Butano cypress grove (CAL FIRE 2023). The robust tap-rooted clumps, unlobed leaves, and presence of two bracts and three bractlets made species identification straightforward (Fig. 1). But while the largest leaves do appear “deeply cordate” when fresh, once mature and drying are more truncate to reniform, and the inflorescences are both “dense” and also a “spike in age,” which made determination to subspecies more challenging (Fig. 1). And the surname coincidence with the author didn't seem to yield any special insights. However, within the current keys and circumscriptions (Hill 2012, 2020), given the large size of the plants (to over 100 cm in diameter), the large, unlobed, crenate leaves (to over 5 cm wide), the three lance-linear bractlets that are shorter than the calyx, and the dense stellate hairs on all (Fig. 1), the plants appear to best fit Sidalcea hickmanii subsp. hickmanii. Associated species include Hesperocyparis abramsiana var. butanoensis, Adenostoma fasciculatum, Arctostaphylos crustacea, Arctostaphylos andersonii A.Gray, Ceanothus cuneatus (Hook.) Nutt., Ceanothus thyrsiflorus Eschsch., Ceanothus papillosus Torr. & A.Gray, Vaccinium ovatum Pursh, Lepechinia calycina, Fremontodendron californicum (Torr.) Coville, Crocanthemum scoparium (Nutt.) Millsp., Eriodictyon californicum, Calystegia purpurata (Greene) Brummitt subsp. purpurata, and Calamagrostis rubescens Buckley (Fig. 1).

Fig. 1.

Sidalcea hickmanii subsp. hickmanii collection site and plant details. A. Burned Butano cypress grove with fire-germinated Sidalcea hickmanii subsp. hickmanii, Crocanthemum scoparium, Fremontodendron californicum, Hesperocyparis abramsiana var. butanoensis, Arctostaphylos crustacea, Calystegia purpurata, Eriodictyon californicum, Ceanothus thyrsiflorus, and Ceanothus papillosus (18 March 2022). B. Second-year Sidalcea hickmanii subsp. hickmanii growing at base of burned Butano cypress trees with Calamagrostis rubescens and Fremontodendron californicum (18 March 2022). C. Inflorescence, showing stellate hairs, bracts and bractlets (18 March 2022). D. Large, unlobed, crenate, leaves on newly growing inflorescence on 18 March 2022. E. Long, mature inflorescences on 14 June 2022. F. Mature plant in peak bloom on 14 June 2022. All photos by author.

Previous knowledge. This species has not been previously recorded on Butano Ridge, including at the Butano cypress grove during multiple pre-fire site visits by the author, and numerous pre-fire site visits and collecting trips by CNPS groups and professional botanists that date back to c. 1895, and include William Dudley, Harry Dutton, Calvin McMillan, Rimo Bacigalupi, and John Silba (Thomas 1958, 1961; CCH2 2023; Himes, CNPS Santa Clara Valley Chapter, personal communication). Sidalcea hickmanii is considered likely to be fire-dependent (Hill 2020), and the combination of historical collection records from the site, McMillan's account of the cypress grove in 1951, historical fire records, local knowledge, and burn signs in the area suggest that the Butano cypress grove may not have burned since 1904, and perhaps longer (McMillan 1952; Verardo and Verardo 1983; CAL FIRE 2023; CCH2 2023; Himes 2023 (pers. comm.)). This possibility could account for the lack of previous local observations, and may imply that the seedbank is very long-lived. The only other known record for Sidalcea hickmanii in the Santa Cruz Mountains was collected in 1998 in coastal scrub near Montara State Beach in northern San Mateo County (S. Seiki s.n., 17 June 1998, DAV394125); this specimen was originally identified as Sidalcea malviflora (DC.) Benth., but then later redetermined as Sidalcea hickmanii Greene subsp. viridis C.L.Hitchcock, Perenn. (CCH2 2023). But based on the visible characters in the high-resolution online image of the herbarium specimen (CCH2 2023), which shows no sign of bractlets, the original determination as Sidalcea malviflora, a species common in coastal scrub in that area (Thomas 1961; Calflora 2023), is likely correct. And this not-uncommon confusion is mentioned in the notes for Sidalcea hickmanii subsp. viridis: “plants reported as subsp. viridis from Mendocino, Sonoma Cos. instead are Sidalcea malviflora (DC.) A.Gray subsp. rostrata (Eastw.) Wiggins, which is similar in its unlobed leaves, but Sidalcea malviflora has no bractlets” (Hill 2012); the notes for Sidalcea malviflora subsp. rostrata also mention that this subspecies is “confused with Sidalcea hickmanii but lacks bractlets” (Hill 2012). Beyond the Santa Cruz Mountains, Sidalcea hickmanii is only found in isolated populations from southern California to southwestern Oregon and appears to have a relict distribution (Hill 2020). Seven subspecies have been described, with six occurring in California and one in Oregon (Hill 2020). The nearest subspecies to the north of the Santa Cruz Mountains is Sidalcea hickmanii subsp. viridis in Marin County, c. 90 km distant and across the Golden Gate (Hill 2020; CCH2 2023), and the nearest to the south is Sidalcea hickmanii subsp. hickmanii in Monterey and San Luis Obispo counties, with the closest occurrence over 100 km from Butano Ridge (Hill 2022; CCH2 2023). Further afield, Sidalcea hickmanii Greene subsp. napensis S.R.Hill occurs in Napa County, Sidalcea hickmanii Greene subsp. pillsburiensis S.R.Hill occurs in Lake County, Sidalcea hickmanii Greene subsp. anomala C.L.Hitchc. occurs in San Luis Obispo County, and Sidalcea hickmanii Greene subsp. parishii (B.L.Rob.) C.L.Hitchc. occurs in San Luis Obispo, Kern and San Bernardino counties (Hill 2020; CCH2 2023).

Significance. The subspecies has a California Rare Plant Rank of 1B.3 (California Native Plant Society 2023), and if the Montara collection S. Seiki s.n., 17 June 1998 (DAV394125) is Sidalcea malviflora, then this Butano Ridge occurrence of Sidalcea hickmanii would be the only known occurrence in the Santa Cruz Mountains bioregion and the four counties that comprise it: San Francisco, San Mateo, Santa Cruz, and Santa Clara. Additionally, Andreasen and Baldwin (2003) suggested that Sidalcea hickmanii is basal within Sidalcea, and Hill (2020) suspects each subspecies may represent a distinct relictual colony. This occurrence of Sidalcea hickmanii subsp. hickmanii appears to be restricted to the same 8–10-acre sandstone area occupied by the Butano cypress, another relict species, even though most of Butano Ridge burned, including many other areas with sandstone, outcrops, and chaparral. This conundrum similarly befuddled McMillan (1952) when he tried to understand why the Butano cypress was restricted to the site: “The cause for the restriction of the cypress to this locality is possibly in part edaphic. The soil is extremely shallow and in many places the sandstone bedrock was exposed or could be exposed by the removal of a few inches of soil. The sharply sloping hillside precludes any great aggregation of soil which might favor the growth of the taller forest. The common occurrence of sandstone exposures along Butano Ridge, however, reveals little reason for the restriction of the cypress to one isolated area.” Indeed, one would think such features would be even less limiting to a plant such as Sidalcea hickmanii. Other fire-followers, such as Arctostaphylos andersonii and Crocanthemum scoparium, germinated at the Butano cypress site and all along Butano Ridge, and thousands of acres of similar chaparral on sandstone substrates burned during the 2020 CZU Lighting Complex Fire. But to date, both Butano cypress saplings and Sidalcea hickmanii have been found only at the remote 8-to-10-acre site. And perhaps just as interesting, the co-occurrence of these rare relicts is apparently not unique. In 2013 Sidalcea hickmanii subsp. parishii was documented for the first time in Kern County as one of the fire-followers that germinated after a grove of Piute cypress, Hesperocyparis nevadensis (Abrams) Bartel, burned on the slopes of Piute Mountain (CNPS Kern Chapter, June 2013, gp10037, Calflora 2023).

A voucher specimen and leaf samples in desiccant were sent to Dr. Bruce Baldwin at UCJEPS for possible future genetic study.