1044. SORBUS PORRIGENTIFORMIS: Rosaceae

Abstract

Sorbus porrigentiformis, GREY-LEAVED WHITEBEAM, is described and illustrated. It is a neoendemic with obovate leaves and fruits wider than long, and it is widespread in south-west England and South Wales. It was originally broadly circumscribed, but it has now been split into at least 11 constituent parts. It is a cornerstone species for Sorbus speciation in Britain. It may have originated from S. aria × S. rupicola or from an ancestral taxon in Central Europe.Sorbus porrigentiformis E.F.Warb., GREY-LEAVED WHITEBEAM (Plate 1044), in its broad sense is the most problematic group of Sorbus L. in Britain (see, e.g., , and it is still being resolved into its constituent parts. English plants with obovate leaves and fruits wider than long were first separated from S. aria (L.) Crantz, COMMON WHITEBEAM, and S. rupicola (Syme) Hedl., ROCK WHITEBEAM, by Hedlund (1914) who included them in his new species S. porrigens Hedl., widely distributed across Europe and Asia Minor. Willmott (1939) typified S. porrigens with a Turkish specimen, and it is no longer accepted as a European taxon (Kurtto et al., 2018). Warburg (1952Warburg ( , 1957 noted that there were distinct morphological differences between the plants in Britain and those in Asia Minor; he separated the British material as S. porrigentiformis, including both triploids and tetraploids, noting that additional subdivisions might be necessary following further studies.After a series of such studies (

1042. SORBUS ARIA: Rosaceae

“…Whether these triploid populations should be treated as a distinct species in Sorbus subgenus Aria [cf., for example, S. porrigentiformis E.F.Warb. (GREY‐LEAVED WHITEBEAM); Rich et al ., 2022a, this issue] remains to be decided, pending the inclusion of samples from Algeria and Morocco. The study of Sosa et al .…”

“…In southwest England, there is a narrow area of overlap between diploid S. aria and tetraploid S. rupicola and S. porrigentiformis in Sorbus subgenus Aria and the diploids S. aucuparia and S. torminalis , leading to the origin of a series of apomictic polyploids, resulting from hybridisation [see, e.g., the account for S. porrigentiformis ; Rich et al . (2022a, this issue)].…”