Crataegus ser. Douglasianae Rehder

Dickinson, Timothy A. & Han, Shery, 2023, What Is Suksdorf’S Hawthorn? Revision Of The Western North American 20 - Stamen Black-Fruited Hawthorns (Crataegus Series Douglasianae, Rosaceae Subtribe Malinae), Journal of the Botanical Research Institute of Texas 17 (1), pp. 151-189 : 173

Crataegus ser. Douglasianae Rehder

TYPE: Crataegus douglasii Lindl. Edwards’s Bot. Reg. 21:t. 1810. 1835.

Description.— Shrubs or small trees up to 10 m tall. Shoots dimorphic, sympodial, vigorous branches (long shoots) often with indeterminate growth during a growing season (thus with both preformed and neoformed leaves) and internodes 2–5 (or more) cm, bearing axillary shoots of determinate growth (short shoots; preformed leaves only) with internodes short (less than 2 cm) or absent. Buds ovoid, reddish brown, shiny, (1–)2–3(–4) mm long. Short shoots frequently developing as thorns, by reduction or suppression of leaf development, sclerification of the axis, and formation of a sharp tip, 5–30(40) mm long, more or less straight, 1.5–4 mm in diameter at the base. Young shoots of the current year orange or brown, glabrous or sparsely pubescent, mature shoots of the previous year vary from reddish brown to red purple, older branches gray or copper-colored. Leaves of flowering and short shoots (microphylls–) notophylls, alternate, simple, blades varying from lanceolate and oblanceolate to more or less elliptic or rhombic-elliptic, 1.5 to 2.5 times as long as wide, up to 10 cm long, glabrous or pubescent at maturity, unlobed or sparsely lobed, sinuses shallow.Venation pinnate, with major secondary veins craspedodromous or semicraspedodromous ( Dickinson & Yan 2021). Short shoot leaves exhibit heteroblastic variation in shape from the shoot base to the tip ( Dickinson & Phipps 1984). Stipules usually caducous, but sometimes persistent on long shoots. Inflorescences terminal, overwintering in bud, almost always on short shoots, bracteate, usually comprising two or more axillary dichasial cymes (the lowermost axillated by a foliage leaf, upper ones by bracts) in addition to the terminal one, thus 10–20 flowered. Pedicels, peduncles and hypanthia glabrous or pubescent. Flowers perfect, regular, epigynous, calyx lobes 5, entire or sparsely toothed, 2.0– 3.5 mm long, petals 5 free, stamens 10–20 free, undehisced anthers pink or cream-colored ( C. douglasii ) at anthesis, styles 4–5, and ovules 2 per locule, superposed. Fruits polypyrenous drupes, purple to black, ellipsoidal to suborbicular (diameters of dry fruits 6–10 mm). Pyrenes single-seeded, the same number as the styles and locules, their radial surfaces pitted or grooved.

Crataegus ser. Douglasianae is distinguished by its fruit color from the red-, orange-, and yellow-fruited members of C. sect. Sanguineae ( C. ser. Sanguineae (Zabel ex C.K. Schneid.) Rehder and ser. Altaicae J. B. Phipps; not C. ser. Nigrae (Loudon) Russanov ). It differs from black-fruited C. ser. Nigrae and C. sect. Salignae in thorn diameter, leaf shape, and geographic distribution.

Distribution.— Western North America (southernmost Alaska, British Columbia, Cypress Hills of Alberta and Saskatchewan, Washington, Idaho, western Montana, Oregon, western Wyoming, northern California), with disjunct occurrences ( C. douglasii ) in the upper Great Lakes basin (Ontario, Minnesota, Wisconsin, Michigan).

Remarks.— See Ufimov and Dickinson (2020) for notes on spelling of the section and series names, and a key to the sections in C. subg. Sanguineae . Other modern descriptions are given elsewhere ( Phipps 2015; Phipps & O’Kennon 2002). Microsatellite, plastome, and nuclear loci sequence data are available as noted here and elsewhere ( Coughlan et al. 2017a; Coughlan 2012; Coughlan et al. 2017b; Liston et al. 2021; Liu et al. 2019; Lo 2008; Lo et al. 2009a; Lo et al. 2007; Lo et al. 2009b; Lo et al. 2010).

Ploidy level.— x = 17 ( Gladkova 1968; Muniyamma & Phipps 1979b), 2 n = 2 x, 3 x, 4 x, 5 x depending on species.