Hypanthium

Abstract: Rosaceae, Rosoideae, Rosa L.; subgenus Eurosa Focke; section Cinnamomeae (DC.) Rehder. Japanese Rose. Rhizomatous multi-stemmed erect deciduous shrub, strongly suckering, mature clones forming impenetrable thickets. Rhizomes woody, with orange-brown cortex and triangulate scale leaves. Rhizome branches and suckers emerge from axillary buds subtended by scale leaves. In addition, suckers may arise from buds on the roots. Stems erect, sometimes arching, to 1.5( − 2) m, often much branched, tomentose when young, densely prickly. Cortex light yellowish brown. Prickles subulate, slender and straight, of all sizes down to acicles. Larger prickles tomentose, at least near the base, and usually glabrous in the apical part. Leaves alternate with (5–)7–9 leaflets contiguous on the rachis. Leaflets nearly equally sized, 2–5 × 1.5–3 cm, leathery and robust, widely elliptical, acute, with broadly cuneate or rounded base. Adaxial side dark green, conspicuously bullate or rugose, rather shiny. Abaxial side green-grey, tomentose to pubescent, with sessile pale glands, and with reticulate nervation. Leaf margin bluntly and simply crenate-serrate, involute, edge of teeth often deflexed. Petiole and rachis densely pubescent, and with many unequal subulate prickles. Stipules pale green, densely pubescent, 2.5 × 1–1.5 cm, divergent, the free part broadly ovate or deltoid. Flowers usually solitary or few together, 6–9 cm across, fragrant, nectarless. Sepals 2–3 cm, entire, with a broad, expanded tip, appressedly pubescent, aciculate and glandular (sometimes with stipitate glands), erect on the hip, persistent. Petals five, bright purplish-pink, sometimes white ( R. rugosa f. alba (Ware) Rehder). Stamens 200– 250 per flower, and styles often more than hundred. Styles pilose; stigmas in a large, domed head, sunk in the narrow, concave disc; disc 2.5–4 mm across; orifice large, at least half the diameter of the disc. A hypanthium (hip) encloses the achenes. It is depressed globose, 1.5–2 cm long and 2–2.5 cm wide, with a distinct neck below the sepals, dull green to orange when unripe, becoming glossy and brilliant red when ripe, most often smooth. Pedicel of the same length as the hip, tomentose, often with gland-tipped acicles, erect in flower, curved in fruit so that the hip points downwards. Achenes with a woody-bony pericarp enclosing the seed. Achenes broadly ovoid, obtusely angular, 4.0–6.0 mm long and 2.0–2.6 mm wide and 1.8–2.2 mm thick, with a distinct suture on both ventral and dorsal sides, hilum basal. Achene surface more or less lustrous, orange-brown. Mean seed (achene) mass is 6.6 mg. The albumen is oily. No subspecies of R. rugosa have been recognized in the British Isles. Despite the many cultivated varieties of the species, mainly forms close to the wild type are seen naturalized. However, naturalized clones may be confused with R. × hollandica (syn. R. × kamtchatica ). This taxon differs morphologically from R. rugosa by having soft-textured, dull leaflets, without prominent veins, less prickly stems, conspicuously glandular sepals, and smaller flowers and hips (Rutherford 1990). Taxonomic position: Rosa L., subgenus Eurosa Focke (syn. subgen. Rosa ), section Cinnamomeae (DC) Rehder (syn. sect. Rosa ; sect. Cassiorhodon Dumort.). Section Cinnamomeae is central in the subgenus Eurosa , which contains all but four of the approximately 150 Rosa species in the world. The diploid species of this section, including R. rugosa , are probably basal in the reticulate evolutionary series from diploid species to irregular polyploid species within this genus (Erlanson 1938; Grossi et al . 1998). Originally introduced as a garden and landscape ornamental, and widely used as rootstock for other cultivated roses, R. rugosa can be found in many different cultivated settings. Now a well-established naturalized alien occurring scattered throughout Britain and invasive in fixed dunes and other coastal habitats.