Hypericum japonicum

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Hypericum japonicum


Annual (? or perennial) herb, 2-45(-50) cm, with stems erect to decumbent or prostrate, un-branched below the inflorescence or also branched from the base or from various parts of the stem, with branches strict or ascending, rooting at the base, 4-lined. Leaves sessile, 2-18 by 1-10 mm, ovate to oblong or elliptic or subcircular or oblong-lanceolate or more rarely oblanceolate or obovate-spathulate, apex obtuse to rounded, base cordate-amplexicaul to cuneate or more rarely attenuate, sometimes glaucous beneath; 1-3 main basal veins, not or scarcely branched, often with 1 or more lateral veins; reticulate venation absent; laminar glands pale, not prominent, small, denser above than beneath; intramarginal glands absent. Inflorescence 1-c. 30-fiowered, cymose and regularly dichasial to monochasial or with branches in uppermost leaf axils, sometimes with subsidiary inflorescences from the next leaf pairs or with branching becoming sympodial and flowers apparently axillary, lax; pedicels exceeding uppermost leaves or not, (1.4-)2-14mm in fruit. Flowers 4-8 mm ø, plane; buds cylindric-ellipsoid, ± obtuse. Sepals 2-5 ½ by ½-2 mm, free, imbricate, narrowly oblong or (rarely) lanceolate to elliptic or obovate, acute or obtuse to rounded, entire, sometimes shortly mucronate, 3-5-nerved, often with ± prominent midrib, especially in fruit; laminar glands pale, linear towards the base, becoming punctate distally; marginal glands absent. Petals pale or bright yellow to orange, 1.7-5 by 0.8-1.8 mm, c. 0.9-1.3 as long as the sepals, elliptic or oblong to obovate, entire, persistent; apiculus absent or vestigial, lateral; laminar and marginal glands absent. Stamens not in apparent fascicles but forming 5 irregular groups when few, 5-30, longest 1½-2.8 mm, 3/5-4/5 as long as the petals; anthers yellow, gland amber. Ovary 1-1½(-1.8) mm, ± broadly ovoid to subglobose; styles (2-)3.0.4-0.8(-l) mm, 2/5-3/5 as long as ovary, ± divergent, gradually broadening towards capitate stigmas; placentas (2-)3, parietal. Capsule (2-)2-½6 by 1.3-2.8 mm, cylindric to globose, not vittate. Seeds yellow-brown, c. ½ mm, cylindric, not carinate, longitudinally ribbed with fine transverse striae.


Asia-Tropical: Australasia: Ceylon: present Japan: present New Zealand: present Pacific:, Hawaiipresent S. Korea: present SE. China: present
Japan, S. Korea and SE. China to Ceylon, Australia, New Zealand and Hawaii; throughout Malesia.


H. japonicum is an extremely variable species; but the variation appears to be continuous, so that, despite the long list of published segregate species or infraspecific taxa, it seems impossible to distinguish infraspecific categories. The following numbered variants, however, will give some idea of the nature of this variation:
  1. Stems erect, simple. Leaves ± broadly ovate, subacute to obtuse, cordate-amplexicaul. Inflorescence terminal only, regularly dichasial at first. Bracts linear. Sepals oblong, acute. Petals as long as sepals. Stamens numerous (25-30). Capsule ± cylindric, shorter than sepals (Korea, China, Philippines).
  2. As type 1, but with subsidiary inflorescences and branches, and often somewhat decumbent habit (S. Japan, Korea, China, India (Assam, Madras), Ceylon, Thailand, Malaya, Sumatra, Java, Celebes, Borneo, Philippines).
  3. As type 1, but inflorescence branching wholly monochasial and stems always ± decumbent (Vietnam, Malaya, Sumatra, Java, Borneo, Philippines).
  4. Differs from type 1 in having some or all the bracts foliar and the habit nearly always decumbent to prostrate, often with diffuse branching. This is found throughout the area of the species. The shape of all parts is very variable, but one characteristic form with obovate outer sepals (var. 'calyculatum') occurs in the Himalaya. Another characteristic form— prostrate with radiating branches, small, obovate to circular leaves and obovate or broadly elliptic sepals—occurs in the western half of Java (Priangan Mts & Dieng).
  5. The stem-branching in this decumbent to prostrate delicate diffuse variant is sympodial (resulting in pseudo-axillary flowers) and the sepals narrowly elliptic to narrowly oblong or oblanceolate (var. humifusurt); the size of all parts is small and the stamens few in number (5-10), and the subglobose capsules exceed the sepals (New Guinea, Tasmania, New Zealand).

H. japonicum has been confused with H. mutilum L., a species mainly of eastern North America that differs from H japonicum in several characters, e.g. the branches are more widely spreading (40-70° from vertical rather than 20-40°), those of the inflorescence being more slender than the stem and main branches (not equally stout), whilst those at the uppermost pair of nodes are usually more or less congested and often sub-umbellate (not roughly equally spaced); also, the bracts and bracteoles are nearly always linear-subulate and about 1-1½ mm long (not broader and/or 2-7 mm long).


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