Sisymbrium leucocladum (Boiss.) D.A. German & Al-Shehbaz, 2018

German, Dmitry A. & Al-Shehbaz, Ihsan A., 2018, A reconsideration of Pseudofortuynia and Tchihatchewia as synonyms of Sisymbrium and Hesperis, respectively (Brassicaceae), Phytotaxa 334 (1), pp. 95-98 : 96-97

Sisymbrium leucocladum (Boiss.) D.A. German & Al-Shehbaz , comb. nov.

≡ Hesperis leucoclada Boissier (1842: 69) ≡ Gynophorea leucoclada (Boiss.) Dvo ř ák (1968a: 111) ≡ Pseudofortuynia leucoclada (Boiss.) Khosravi (2003: 20) . Described from: “[Aucher-Eloy] N. 4123, Ispahan.” Lectotype (designated by Dvo ř ák (1968a: 105; 1968b: 269): IRAN. Ispahan [Isfahan]. Aucher-Eloy 4123. W-0050812!; isolectotypes: BM-000522181!, BM-000522182!, G-BOIS-00332220!, G-00446088!, G-00446989!, G-BOIS-00332220!, K-000693872!, KW!, LE-00013085!, P- 02272565!, P- 02272566!, P- 02272567!).

= Sisymbrium hesperidiflorum Boissier & Buhse (1860: 22) . Described from: “Im Gebirge von Jesd [Yazd], Thal Derrehgoum, 23 April 1849 (florens et fructiferum). [Buhse] No 1296.” Type:?

Note. No material of S. hesperidiflorum was found in G and LE and neither JSTOR not other databases provide any relevant information. The name is treated as conspecific with S. leucocladum based on the synonymy proposed by Boissier (1867), the author of both S. hesperidiflorum and H. leucoclada , and by an analysis of their protologues which fully match each other.

= Pseudofortuynia esfandiarii Hedge (1968: 57) . Described from: “Inter Abadeh et Dowlatabad, 1500–2000 m, 26. 4. 1956, Schmid 5335, Holotypus W!, Isotypus G.” Type: W-19590022415!; isotypes E-00135544!, G-00371875!

2. Tchihatchewia Boiss.

Family-wide molecular phylogenetic study by Warwick et al. (2010) provided strong support for the monophyly of the tribe Hesperideae which included Hesperis matronalis Linnaeus (1753: 663) , H. sibirica Linnaeus (1753: 663) , and Tchihatchewia isatidea Boiss. ( Tchichatscheff 1860: 292). Their results clearly show that the monospecific Tchihatchewia is nested within the larger and earlier-published Hesperis and, therefore, the two genera ought to be united as done herein, and the species below transferred to the latter genus. The main problem for the failure to do such a transfer in the past was the bizarre fruit morphology of T. isatidea . The species has broadly winged, 1- or 2- seeded, latispetate, indehiscent silicles and flattened seeds with accumbent cotyledons (Tchihatcheff 1860, Appel & Al-Shehbaz 2003), whereas species of Hesperis are characterized by wingless, predominantly many-seeded, terete to subquadrangular, dehiscent siliques, and plump seeds with incumbent cotyledons ( Busch 1939, Tan & Suda 2002). However, fruit morphology in Hesperis is quite diverse (Dvo ř ák 1968b, 1972, 1973) and, with a single exception of a fruit being a silicle, all features of Tchihatchewia can be found separately or in various combinations in some SW Asian representatives of Hesperis . In particular, according to Dvo ř ák’s (1973) classification, indehiscent siliques occur in two out of five subgenera including all five species of H. subgen. Diaplictos (Dvo ř ák 1968b: 271) Dvo ř ák (1973: 267). Clearly latiseptate fruit characterize H. breviscapa Boissier (1842: 67) , H. kotschyi Boissier (1856: 21) , and H. thyrsoidea Boissier (1867: 234) , representing another two subgenera of Dvo ř ák (1973). A tendency of reduction of the number of seeds is also revealed in H. breviscapa and especially in H. thyrsoidea having just 3 or 4 seeds per fruit ( Boissier 1867) which are visibly compressed. Besides, the latter species is peculiar for its silique being remarkably expanded (as if narrowly winged) around the seeds and twisted at maturity; this is the only representative of Hesperis for which accumbent cotyledons are reported (Dvo ř ák 1973). In this and in a number of other species of Hesperis , siliques also strongly reflexed just as in Tchihatchewia .

Every other morphological aspect of Tchihatchewia isatidea , including important diagnostic features such as the indumentum of a mixture of long simple setose and smaller stalked branched trichomes, large fragrant flowers with closed bisaccate calyx and long-unguiculate petals, flattened filaments of inner stamens, deeply bilobed stigmas, non-margined seeds ( Schulz 1936, Cullen 1965, Appel & Al-Shehbaz 2003), etc., fits the description of Hesperis . Hence, a merger of Tchihatchewia with Hesperis does not drastically (in fact, only slightly) change the characteristics of the latter genus as it might initially seem. Evolutionary plasticity of the fruit of Brassicaceae is a well-known phenomenon and silicles of Tchihatchewia most likely represent recent apomorphy within Hesperis , as can be assumed from their structure. Indeed, the wing disregarded, “the fruit [of T. isatidea ] itself is elongated-elliptic” ( Schulz 1936: 482, originally in German), and when mostly developed, 2-seeded, it is even lanceolate-linear and quite reminding somewhat shortened, also gradually tapered upward silique of H. breviscapa or H. kotschyi with subglobose stigma similar to that of Tchihatchewia . Summing up, it is obvious that the single difference between T. isatidea and species of Hesperis is insignificant to warrant the recognition of the former as independent monospecific genus that evolved within Hesperis .