Phemeranthus sediformis

Within the range of P. sediformis, it is found at elevations between 800–1,500 m (2,600–4,900 ft) on south to southwesterly facing slopes. The preferred habitat is on the eroding edges and slopes of hills and mountains where broken up rocky outcroppings are exposed. In these areas the plants colonize well-drained shallow soils derived from weathered volcanic rock. The regosols of these habitats are noted to be similar to the serpentine soils that other Phemeranthus species prefer. The climate is considered to be a mild continental climate where the overall temperature range in a year is about 25 °C (77 °F). The most northerly sites in the region of Kamloops experience seasonal lows around −6 °C (21 °F) during winter, while the summer high temperatures are an upper average of 20.9 °C (69.6 °F). While precipitation is spread fairly uniformly over the year, there are small peaks in the early summer and in the winter. It has been suggested that the occurrences of rain from summer afternoon thunderstorms may play a factor in the lower elevational limits of the plants. Under this theory, there is too much precipitation evaporating before it reaches the ground below 800 m (2,600 ft) to allow the plants to survive the dry conditions during the summer months. Within the Kettle River Range of Washington, P. sediformis is a noted component of the Douglas's buckwheat/Sandberg's bluegrass floral community. This community is restricted to loam soils that are derived from or impacted by surface weathered andesite rock, and are restricted in range due to the relatively rare occurrence of soils in the region. Plants within the community include the shrubby mountain big sagebrush and the perennial herbs arrowleaf balsamroot, arrowleaf buckwheat, bigseed biscuitroot, bitterroot, brittle bladderfern, blue bunchgrass, bluebunch wheatgrass, deer paintbrush, Holbøll's rockcress, limestone hawksbeard, meadow death camas, narrow leaved fleabane, nodding microseris, parsnip-flower Buckwheat, tufted phlox, upland larkspur, wallaces spikemoss, wyeth biscuitroot, and yellow fritillary.

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Specimens of Phemeranthus sediformis were collected by Scottish botanist John Jeffrey during his visit to the southern interior of British Columbia in 1851. Hired by a Scottish group known as the "Oregon Botanical Association" to continue the botanical work of David Douglas and extend the work beyond the areas explored by Douglas, in 1850 Jeffrey had arrived in British Columbia and after overwintering had crossed the British Columbian Rocky Mountains to reach the Columbia River. He travelled downstream along the Columbia to the Okanogan River and then north up that river to the "Seme-ke-mele" (Similkameen) region, arriving at the junction of the Similkameen and Tulameen Rivers by July 9. On July 15, 1851 (misreported by Poellnitz as June 15), somewhere along the Similkameen River, Jeffrey collected what would become the holotype for Phemeranthus sediformis. It was shipped with the other botanical material collected back to Scotland and likely dispersed to members of the Oregon Botanical Association. The P. sediformis specimen was eventually deposited in the Kew Herbarium Hookerianum collections as specimen K000641679 in 1867. The specimen was not described and named in detail until 1933 when German botanists Karl von Poellnitz [de] described a number of succulent species. He placed the new species into the genus Talinum while noting that the current descriptions of species prevented him from accepting the division of the genus into the sections Phemeranthus and Talinastrum. On May 27–28, 1933, the same year that Poellnitz described his species, United States Army Corps of Engineers botanist Carl S. English Jr. collected several specimens of the same plant from two locations in Washington State. Both plants were found in the mountainous Okanogan Highlands area of Okanogan County, on Fir Mountain at 5,666 ft (1,727 m), and on the ridge west of the Granite Creek/Sweet Creek confluence near the eastern edge of the county. The plants were transplanted to the garden of English's Seattle-area home and the specimen he chose to use in describing what he thought would be a new species came from the garden on August 10, 1933. English published his October 2, 1934, description of Talinum okanoganense in the Proceedings of The Biological Society of Washington. This was the binomial by which the species was most frequently known until Robert W. Kigers's 2001 revision of the species. At the same time that English was working on his paper, Canadian–American botanist Alice Eastwood was also working on plants from the Columbia Mountains. While exploring the area around Brigade Lake south of her home in Kamloops during 1924, K. C. Way came across a population of the plants and collected a number that she transplanted into her yard as a rockery garden. Over the next decade Way traded and gifted plants to homes across the Northwest. On a separate collecting trip she explored the slopes of Mount Baldy northeast of Osoyoos, where she collected specimens which she traded to Charles W. Armstrong. Based on specimens that came to her from Armstrong, proprietor of Van Stone Gardens in Vancouver, Eastwood described her new species. The formal description was based on a traded plant that later flowered in the California Academy of Sciences botanical garden. The plant was then collected as the holotype and added it to the herbarium collection as specimen number 216937. She published her formal description in the November 1934 issue of the journal Leaflets of Western Botany just two months after English's description appeared, making it a synonym of his species. By the late 1990s, the monophyletic nature of genus Talinum was in question. Phemeranthus had been treated as a section within Talinum traditionally, and since the description of the type species, Phemeranthus teretifolius, other North American species had been described and placed into the section. The North American species all presented a number of characters in common that were not seen in the old world species. Robert W. Kiger reviewed the North American Talinum species in 2001 as a preparation for the publication of the Flora of North America section on Portulacaceae. He deemed that nearly all the valid species were in fact distinct enough as a group to raise Phemeranthus to the status of full genus. Among the revisions to the species, Kiger noted that Poellnitz's P. sediformis had nomenclatural priority over English's and Eastwood's names, which he listed as junior synonyms. Kiger attempted to locate Poellnitz's holotype herbarium specimen, but was not able to do so at that time due to his assumption that the specimen was part of the Berlin Botanical Garden and Botanical Museum. He was able to locate one of the isotype sheets in the Kew collections.

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