Hypericum is a genus with about 370-460 species, mostly native to the temperate areas of the Old and New World (some also on mountains in the tropics). Twelve species are native in Belgium: Hypericum androsaemum L. (see, however, below), H. desentangsii Lamotte, H. dubium Leers, H. elodes L., H. hirsutum L., H. humifusum L., H. linariifolium Vahl, H. maculatum Crantz, H. montanum L., H. perforatum L., H. pulchrum L. and H. tetrapterum Fries. Out of these, Hypericum androsaemum is extremely rare as a native species and only known from a small, rather disjunct area in Wallonia (Saintenoy-Simon 1985). It is much more frequent in cultivation and increasingly occurs as a garden escape or throw-out on refuse tips, in wood margins, etc. It is also present as a relic in old parks or near castles. Its berries are probably eaten by birds and subsequently dispersed to any suitable habitat. This way, it has in recent years considerably extended its distribution range in Belgium. Especially in parts of West-Flanders (e.g. in the wide surroundings of Kortrijk) it has become a rather common species in undergrowth of deciduous woodland. Hypericum lineariifolium was only recently recorded for the first time in Belgium (Clesse & Duvigneaud 1987). It occurs in a single, natural locality near Petigny (very disjunct from its area in southwestern Europe) but is believed to be native, although this record was not taken into account in Robson’s monographic study of this section (Robson 2010a). Identical records in the British Isles are also accepted as disjunct but native. Some of the other native species are sometimes recorded outside of their natural distribution range: Hypericum hirsutum has been observed as an introduction with timber or rocks and is locally more or less naturalized (known since the 1980’s, for instance, from a railway siding in Ingelmunster). Interestingly, a population of the rare Hypericum montanum was discovered by a track in woodland in Averbode in 2012 and seems to persist well. It was doubtlessly introduced there.
Numerous species (incl. cultivars and hybrids) of Hypericum are grown as ornamentals, mainly for their showy flowers but also for ground-cover (strongly rhizomatous perennials). An extensive and up-to-date account of the genus Hypericum in cultivation is provided by Robson (1995). See also Robson (1985) for more details. In these accounts more than 120 species are dealt with.
The cultivated and escaped shrubby representatives of Hypericum are surely poorly understood in Belgium. In addition to the taxa treated below several others are widespread in cultivation and doubtlessly occur as escapes. More or less common garden plants include Hypericum forrestii (Chitt.) N. Robson, H. hircinum L., H. pseudohenryi N. Robson, H. xylosteifolium (Spach) N. Robson and others. The account in Robson (1985) deals with most of these shrubby species (wild as well as cultivated, including hybrids and cultivars) and is particularly helpful.
More useful information about the genus Hypericum, including lots of bibliographic items, is stored at ‘Hypericum online’ at: http://hypericum.myspecies.info/.
1 Stem densely pubescent (native) === Hypericum elodes and H. hirsutum
Stem (sub-) glabrous === 2
2 Evergreen to deciduous shrubs, woody in the lower half. Glands on leaves, sepals and petals translucent and inconspicuous === 3
Herbaceous perennials or (rarely) low shrubs. Glands on leaves, sepals and/or petals, at least in part, black === 7
3 Styles 5. Flowers ca. 40-80 mm across. Stamens shorter than sepals. (Semi-) evergreen, strongly rhizomatous === 4
Styles 3. Flowers ca. 15-30 mm across. Stamens ca. as long as sepals. Deciduous, non-rhizomatous === 6
4 Stem creeping and rooting === Hypericum calycinum
Bushy, erect perennial, not creeping and rooting === 5
5 Anthers brick-red, with stamens at least half as long as petals. Stems low arching, rarely more than 50 cm tall. Leaves usually apiculate === H. ×moserianum
Anthers orange-yellow, with stamens at most half as long as petals. Stems arching and spreading, up to 175 cm tall. Leaves not apiculate === H. ×hidcoteense
6 Fruit a black berry when ripe (not dry), indehiscent. Petals at most as long as sepals. Styles ca. ½ as long as ovary. Leaves 70-120 mm long, ovate. Stem distinctly winged, wings undulate below nodes (native) === H. androsaemum
Fruit a more or less dry capsule when ripe, opening with 3 valves (or more or less indehiscent), bright red turning brown. Petals 1,5-2x as long as sepals. Styles distinctly longer than ovary. Leaves 30-90 mm, ovate to oblong-lanceolate. Stem without or with indistinct, non-undulate wings below nodes === H. ×inodorum
7 Stem with 4 ridges (native) === H. desentangsii, H. dubium, H. maculatum and H. tetrapterum
Stem terete or with 2 ridges === 8
8 Sepals strongly imbricate. Corolla up to 6 cm across. Plant glaucous and bushy, becoming woody at base === H. olympicum
Sepals not imbricate. Corolla not exceeding 25 mm across. Plant never glaucous, bushy and woody at base (native) === H. humifusum, H. linariifolium, H. montanum, H. perforatum and H. pulchrum
Clesse B. & Duvigneaud J. (1987) Présence d'Hypericum linarifolium Vahl en Belgique. Dumortiera 37: 9-13.
Fröberg L. (2010) Hypericum. In: Jonsell B. & Karlsson T. (eds.), Flora Nordica, vol. 6. The Swedish Museum of Natural History, Stockholm: 5-12. [available online at: http://www.floranordica.org/Review/-Review_public/accounts/Hypericaceae.html#olympicum]
Gillet J.M. & Robson N.K.B. (1981) The St. John's-Worts of Canada (Guttiferae): IV + 40 p.
Jäger E.J., Ebel F., Hanelt P. & Müller G. (eds.) (2008) Rothmaler Band 5. Exkursionsflora von Deutschland. Krautige Zier- und Nutzpflanzen. Springer Verlag, Berlin: 880 p.
Lambinon J. & Verloove F. (2012) Nouvelle Flore de la Belgique, du Grand-Duché de Luxembourg, du Nord de la France et des Régions voisines (Ptéridophytes et Spermatophytes). Sixième édition. Jardin botanique national de Belgique, Meise: CXXXIX + 1195 p.
Lancaster R. & Robson N. (1997) Bowls of beauty. Garden (London) 122: 566-571.
Li X. & Robson N.K.B. (2007) Hypericum. In: Wu Z.Y. & Raven P.H. (eds.), Flora of China, vol. 13. Science Press, Beijing & Missouri Botanical Garden Press, St. Louis: 2-35. [available online at: http://flora.huh.harvard.edu/china/PDF/PDF13/Hypericum.pdf]
Ramos-Núñez Á.F. (1993) Hypericum. In: Castroviejo S. & al. (eds.), Flora Iberica, vol. 3. Real Jardín Botánico, Madrid: 157-185. [available online at: http://www.floraiberica.es/floraiberica/texto/pdfs/03_058_01_Hypericum.pdf]
Nürk N.M. (2011) Phylogenetic analyses in St. John’s wort (Hypericum) Inferring character evolution and historical biogeography. PhD thesis, Freien Universität Berlin. [available online at: http://www.diss.fu-berlin.de/diss/servlets/MCRFileNodeServlet/FUDISS_derivate_000000010425/Dissertation_Nuerk_epub.pdf]
Robson N.K.B. (1968) Hypericum. In: Tutin T.G. & al. (eds.), Flora Europaea, vol. 2. Cambridge University Press, Cambridge: 261-269.
Robson N.K.B. (1977) Studies in the genus Hypericum L. (Guttiferae), part 1. Bull. Brit. Mus. Nat. Hist. 5: 291-355.
Robson N.K.B. (1981) Studies in the genus Hypericum L. (Guttiferae), part 2. Bull. Brit. Mus. Nat. Hist. 8: 55-226.
Robson N.K.B. (1985) Studies in the genus Hypericum L. (Guttiferae), part 3. Bull. Brit. Mus. Nat. Hist. 12: 163-325.
Robson N.K.B. (1987) Studies in the genus Hypericum L. (Guttiferae), part 7. Bull. Brit. Mus. Nat. Hist. 16: 1-106.
Robson N.K.B. (1990) Studies in the genus Hypericum L. (Guttiferae), part 8. Bull. Brit. Mus. Nat. Hist. 20: 1-151.
Robson N.K.B. (1995) Hypericum. In: Cullen J. & al. (eds.), The European Garden Flora, vol. 4. Cambridge University Press, Cambridge: 44-74.
Robson N.K.B. (1996) Studies in the genus Hypericum L. (Guttiferae), part 6. Bull. Nat. Hist. Mus. London 26: 75-217.
Robson N.K.B. (2001) Studies in the genus Hypericum L. (Guttiferae), part 4(1). Bull. Nat. Hist. Mus. London 31: 37-87.
Robson N.K.B. (2002) Studies in the genus Hypericum L. (Guttiferae), part 4(2). Bull. Nat. Hist. Mus. London 32: 61-123.
Robson N.K.B. (2006) Studies in the genus Hypericum L. (Clusiaceae). Section 9. Hypericum sensu lato (part3): subsection 1. Hypericum series 2. Senanensia, subsection2. Erecta and section 9b. Graveolentia. Syst. Biodivers. 4: 19-98.
Robson N.K.B. (2010a) Studies in the genus Hypericum L. (Hypericaceae) 5(1). Sections 10. Olympia to 15/16. Crossophyllum. Phytotaxa 4: 5-126.
Robson N.K.B. (2010b) Studies in the genus Hypericum L (Hypericaceae) 5(2). Sections 17. Hirtella to 19. Coridium. Phytotaxa 4: 127-258.
Robson N.K.B. (2012) Studies in the genus Hypericum L. (Hypericaceae). 9. Addenda, corrigenda, keys, lists and general discussion. Phytotaxa 72: 1-111.
Robson N.K.B. (2015) Hypericum. In: Flora of North America Editorial Committee (eds.), Flora of North America North of Mexico, vol. 6. Oxford University Press, New York: 72-102. [available online at: http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=116180]
Robson N.K.B. (2016) And then came molecular phylogenetics—Reactions to a monographic study of Hypericum (Hypericaceae). Phytotaxa 255: 181-198.
Saintenoy-Simon J. (1985) La distribution et l’écologie d’Hypericum androsaemum L. en Belgique. Nat. Mosana 38(1): 11-17.
Stace C. (2010) New flora of the British Isles, 3th ed.: XXXII + 1232 p. Cambridge University Press.