Revision of the Maddenia clade of Prunus (Rosaceae)

Abstract The Maddenia clade of Prunus L. is monographed based on herbarium and field studies. Four species are currently accepted in this group: Prunus himalayana J.Wen, Prunus hypoleuca (Koehne) J.Wen, Prunus hypoxantha (Koehne) J.Wen, and Prunus gongshanensis J.Wen, with the last described herein as a new species. Maddenia fujianensis Y.T.Chang and Maddenia incisoserrata T.T.Yü & T.C.Ku are treated as synonyms of Prunus hypoleuca.


Introduction
Th e Maddenia group has been shown recently to be nested within Prunus L., a genus with many economically important fruit crops and ornamental plants, such as almond and cherry blossom (Wen et al. 2008). Chin et al. (2010) showed Maddenia Hook.f. & Th omson as a monophyletic group closely allied with the temperate members in subgenera Laurocerasus and Padus of Prunus, and they transferred species of Maddenia to Prunus. Th e Maddenia clade contains a small group of trees distributed in temperate regions of the Himalaya and eastern to western China (Rehder 1940;Yü et al. 1986;Chin et al. 2010).
Hooker and Th omson (1854) described the genus Maddenia in honor of Major E. Madden for his contribution to the botany of the Himalayan regions. Maddenia was distinguished from Prunus based on its fl owers with ten tepaloid perianth segments, i.e., petals not diff erentiated from sepals (Rehder 1940). Th e variable number of indistinguishable perianth segments was used as a diagnostic character for the approximately 40 paleotropical species of Pygeum Gaertn. (Backer and Bakhuizen van den Brink 1963). Nonetheless, Kalkman (1965) considered this undiff erentiated perianth in Pygeum as an overlapping character with Prunus, which prompted him to transfer Pygeum species into Prunus subgenus Laurocerasus (Duhamel) Rehder (specifi cally to section Mesopygeum (Koehne) Kalkman).
Maddenia himalaica Hook.f. & Th omson was the fi rst species described in this group. Hooker and Th omson (1854) pointed out that this plant had dimorphic fl owers with 10 perianth segments and one or two pistils. Th e authors noted that this species of their new genus resembled Pygeum in its fl owers and Cerasus in its foliage and drupe (Hooker and Th omson 1854). Maddenia pedicellata Hook.f. was the second described species, which diff ered from M. himalaica in its much longer pedicels (Hooker 1879 Chang (1985) described M. fujianenesis Y.T.Chang, which diff ered from M. hypoleuca in M. fujianensis' looser raceme and its rusty tomentose infl orescence axis, pedicels and bracts. Maddenia incisoerrata T.T.Yü & T.C.Ku was described by Yü et al. (1985) as being similar to M. hypoxantha and M. wilsonii except that M. incisoserrata had abaxially glabrous leaves with deeply serrate margins and shorter and denser racemes.
Th e morphological diff erences among the species mostly concern pubescence and color on the abaxial leaf surface, teeth on the leaf margin, and the raceme length and density (Koehne 1911;Lu et al. 2003). However, species delimitations in Maddeina have been controversial and identifi cations of the Maddenia group of species are often extremely diffi cult in the fi eld or in the herbarium, especially concerning M. hypoleuca and M. incisoserrata, and M. hypoxantha and M. wilsonii (J. Wen, pers. observ.). Koehne (1911) emphasized leaf pubescence and Lu et al. (2003) used size of bud scales, stipule shape and bract shape to separate M. hypoxantha and M. wilsonii. Hara (1976) stated that Maddenia himalaica var. glabrifolia was similar to M. hypoleuca in leaf pubescence, and suggested treating M. hypoleuca possibly as a variety of M. himalaica. In addition, Hara (1976) pointed out that a part of the holotype of M. pedicellata was not Maddenia, but belonged to the Cerasus subgroup of Prunus. Chang (1985) used fl ower density of the raceme to separate M. fujianensis from M. hypoleuca; and Yü et al. (1985) used leaf pubescence, leaf margin, and raceme length to diff erentiate M. incisoserrata from M. hypoxantha and M. wilsonii. Lu et al. (2003) separated M. hypolecua, M. incisoserrata and M. fujianensis based on their leaf color and size, number of veins, and teeth on margin.

Methodology
About 350 herbarium specimens from A, BM, CAS, CDB, E, GH, IBSC, K, KUN, L, MO, NY, PE and US were examined. We also conducted fi eld studies in Fujian, Gansu, Hubei, Sichuan, Xizang and Zhejiang provinces of China. We herein provide a description of the Maddenia clade of Prunus, a key to all four species of the clade we recognized, and descriptions of each species.

Key to species of the
Distribution. Western to central China. Discussion. Koehne (1911) Koehne (1911) indicated that the holotype of M. hypoxantha (E.H. Wilson 909, A) was a mixed collection of M. hypoxantha and M. wilsonii. We examined the specimen and found that the diff erences between the two branches on the same sheet seem to be extremely indistinguishable. Lu et al. (2003) used size of bud scales, stipule shape, stipule appearance and bract shape, to separate the two "species". We found that it is diffi cult to use these characters to consistently separate the two "species". We herein treat Maddenia wilsonii as a synonym of Prunus hypoxantha. ( Maddenia fujianensis Y.T. Chang (Guihaia 5: 25. 1985). Prunus fujianensis (Y.T.Chang) J. Wen (Bot. J. Linn. Soc. 164: 243. 2010). Type: China. Fujian: Chong An Xian, Xing Chun, Shan Gang, Huang-Gang-Shan, in sparse forest, 1700 m, shrub  Discussion. Yü et al. (1985) stated that Prunus incisoserrata was similar to P. hypoxantha and M. wilsonii except that the leaves of P. incisoserrata are abaxially glabrous; the margin is deeply serrated; and infl orescence is shorter and denser. Th e character of glabrous abaxial leaf blade is similar to that of P. hypoleuca. We also observed variations in the depth of the leaf teeth and infl orescence length of specimens of Maddenia incisoserrata and Prunus hypoleuca. In fact the type specimen of P. hypoleuca bears leaves with deeply serrated teeth at the margin. Chang (1985)  Description. Small trees 4-8 m tall. Branches purple, shiny glabrous; branchlets of fi rst year's growth pubescent. Winter buds purplish brown, ovoid; scales to 4-20 × 3-15 mm, ovate, outside brown pubescent but glabrescent. Stipules lanceolate to broadly so, 12-25 × 2-8 mm, membranaceous, margin with glandular teeth, apex acuminate to acute. Petiole 2.5-5 mm, brownish pubescent. Leaves oblong, elliptic to ovate, 5-13 × 2-6 cm, abaxially light green, nearly glabrous, only pubescent on lateral vein axils, adaxially dull green and glabrous, margin doubly irregularly serrate at the upper 2/3, glandularly serrulate at the lower 1/3, teeth at the margin sharp, apex acuminate, base subcordate to broadly cuneate; secondary veins 20-24 on either side of midvein. Racemes 4-6 cm, brown pubescent, 12-16 fl owered; bracts lanceo-