Hypericaceae

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Hypericaceae

Description

Trees, shrubs or perennial or annual herbs. Leaves simple, opposite and decussate (Mal. spp,), entire (Mal. spp.), sessile to shortly petioled, often with ± translucent and sometimes black or red glandular dots and/or lines. Stipules 0. Inflorescences terminal and sometimes axillary, very rarely axillary only, cymose to thyrsoid or rarely racemose, bracteate at least initially, l-∞ -flowered. Flowers bisexual, actinomorphic, homostylous or heterodistylous. Sepals 5 (Mal. spp.), free or ± united, imbricate, entire or with margin variously divided and often glandular, lamina glandular like the leaves, usually with greater proportion of glands linear rather than punctiform, persistent (Mal. spp.). Petals 5 (Mal. spp.), free, imbricate (contorted), alternisepalous, entire or with margin variously divided and often glandular, lamina usually glandular like the leaves, sometimes with nectariferous basal appendage, glabrous (Mal. spp.), caducous or persistent. Stamen fascicles 5 (Mal. spp.), epipetalous, free or variously united, each with l-∞ stamens; filaments variously united or sometimes apparently free, the free part usually slender; anthers 2-thecal, dorsifixed, often with gland terminating connective. Staminodial fascicles 3 or 0 (Mal. spp.), when present alternating with stamen fascicles. Ovary 1, superior, 5-3-celled or 1-celled with 5-2 parietal placentas; styles 5-3 (2), free or ± united, ± slender; stigma punctiform to capitate; ovules ∞-2 on each placenta (Mal. spp.), anatropous, horizontal or ascending. Fruit capsular (Mal. spp.), dehiscing septicidally or loculicidally. Seeds ∞- on each placenta, sometimes winged or carinate; embryo cylindric, straight or curved, with cotyledons longer to shorter than hypocotyl; endosperm absent.

Distribution

Africa: present America: present Arctic regions: present Asia-Tropical: E. Asia: present Indo-Malesia: present Madagascar: present NE. America: present Polynesia: present tropics and immediately adjacent areas: present
There are 7 genera with c. 550 spp., cosmopolitan except for Arctic regions and most of Polynesia, but only Hypericum and Triadenum occur outside the tropics and immediately adjacent areas. Of the three tribes, the Vismieae (3 genera) occur in Africa (including Madagascar) and America, the Cratoxyleae (3 genera) in Madagascar, Indo-Malesia, E. Asia and NE. America, and the Hypericeae (Hypericum) throughout most of the range of the family except for most lowland tropical areas. In Malesia only two genera are present: Cratoxylum Bl. and Hypericum L.

Pollination

Flowers of Hypericum are nearly all open-pollinated, being visited only for pollen by e.g. Syrphid flies and Bombus spp. Specialized pollination with nectar secretion and sometimes dimorphic heterostyly has evolved twice in Hypericum and also occurs in Cratoxylum and Eliaea (see below, under Morphology).

Dispersal

Seeds of the Hypericeae and Cratoxyleae are small and sometimes have wing-like expansions of the testa which would tend to promote wind dispersal. Those without such an aid are normally dispersed by gravity; but the seeds of some species of wet habitats may be carried in mud on the feet of wading birds. Birds or other animals are instrumental in the dispersal of those few species of Hypericum (in four distinct parts of the genus) in which the normally capsular fruit has become ± baccate, as well as those of the Vismieae, where the fruit is always baccate or drupaceous.

Morphology

The three tribes of the Hypericaceae can be distinguished by several floral characters, as follows:
  • Vismieae: Perianth 5-merous; petals adaxially pubescent; staminodial fascicles 5; stamen fascicles 5; ovary 5-merous; fruit baccate or drupaceous.
  • Cratoxyleae: Perianth 5-merous; petals glabrous; staminodial fascicles 3; stamen fascicles 3 (i.e. 2 +2 + 1); ovary 3-merous; fruit capsular.
  • Hypericeae: Perianth 5- 4-merous; petals glabrous; staminodial fascicles absent or very rarely 3; stamen fascicles 5-4 (free or variously grouped or united); ovary 5-2-merous; fruit capsular or rarely baccate.


The grouping of the stamens has attracted much attention. (For a discussion of this question see , and works cited therein). Evidence from morphology, vascular anatomy and ontogeny indicates that in this family as well as the Guttiferae, the androecium basically comprises two diplostemonous whorls of stamen fascicles. In the Hypericaceae the episepalous fascicles are sterile or absent, whereas the epipetalous ones are fertile and may be free (Vismieae, Hypericum pro parte), united 2+2 + 1 (Crat-oxyleae, Hypericum pro parte) or all united (Hypericum pro parte). The individual filaments of each fascicle may be united for over ⅔ of their length or less; or they may arise independently from the receptacle, so that the androecium appears to be afascicular. The number of stamens in each fascicle varies from 80-100 to 1 in Hypericum, plants with an androecium in the latter state typifying the genus Sarothra L., which LINNAEUS placed in his group Pentandria. These, however, cannot be recognized as distinct from Hypericum.

Some species of Cratoxylum, and some specimens of the monospecific genus Eliaea, have an appendage at the base of the petal ('petal scale') which encloses nectariferous tissue (cf. ), and some of these exhibit dimorphic heterostyly, indicating a trend towards specialized insect pollination. This pollination syndrome also occurs exceptionally in Hypericum (see ROBSON, l.c.). It is associated with stiff erect sepals, resulting in an effectively tubular corolla. In such flowers, HOCHREUTINER (l.c.) has shown that the sterile episepalous stamen fascicles ('hypogynous scales') may act like lodicules by swelling and thereby expanding the perianth whorls.

Anatomy

Research on the anatomy of the Hypericaceae has been summarized in METCALFE & CHALK (), while a more detailed discussion of floral and vegetative anatomy of the genera Eliaea and Cratoxylum will be found in P. BAAS (). Some of the most important anatomical papers for systematic purposes concern the nature and distribution of the secretory system that is found throughout the Hypericaceae and Guttiferae. Owing to a photosensitive reaction induced by hypericin ('hypericism'), the bio-chemistry of this and related substances, as well as the clinical details, have been much studied (review in ). The most recent summaries of the biochemical studies on hypericin and its distribution in Hypericum, both morphologically and systematically, are by C. MATHIS & G. OURISSON () and C. MATHIS (). The form and distribution of 'black' glands has proved to be of taxonomic importance in Hypericum, while in Cratoxylum the form of the glands in the petals is of sectional significance. Other recent papers concerning anatomical topics in the Hypericaceae are few, but that by E. K. SCHONFIELD (), on petiole anatomy in the Guttiferae and related families, may be mentioned.

Taxonomy

The tribes Vismieae, Cratoxyleae and Hypericeae are frequently treated as the subfamily Hypericoideae of the Guttiferae, from which they differ by no one constant character, and so the rank of subfamily may well be the most appropriate one. The combination of the following characters, however, make it immediately recognizable:

Flowers bisexual. Antesepalous stamen fascicles sterile or absent; epipetalous fascicles free or variously united; stamens with filaments slender, free or partly united, and anthers small, dehiscing longitudinally. Ovary with styles 2-5, ± elongate, free or partly or rarely wholly united and placentae 2-5, axile to parietal, each with l-∞ ovules. Fruit capsular or baccate or drupaceous. Seeds exarillate; embryo with cotyledons free, not incrassate, and hypocotyl ± slender. Germination epigeal. Leaves usually with venation ± reticulate; glandular canals often interrupted or replaced by globular lacunae ('punctate glands'), often coloured dark red or black by hypericin.

Cytology

The basic chromosome number for the Hypericeae (i.e. Hypericum) appears to be n = 12, from which there is a descending series along several separate evolutionary lines to n = 7 or, possibly, 6 (). Tetraploids occur on all the base numbers; but the only higher degrees of 'ploidy' recorded (pentaploidy and hexaploidy in H. perforatum L. and its hybrids) are associated with a partially apomictic breeding system. Only four species in the other two tribes have known chromosome numbers; two unspecified species of Vismia (Vismieae) have n = 10, whereas in the Cratoxyleae, Cratoxylum formosum (JACK) DYER has n = 7 and Triadenum virginicum (L.) RAFIN. n = 19. Structural hybridity occurs in two American species of Hypericum, H. punctatum LAMK and H. mitchel-lianum RYDB. ().

Phytochemo

Hypericaceae were treated as Guttiferae-Hypericoideae in my , to which the reader is referred for references of work published before 1965.

Our chemical knowledge of Hypericaceae is based largely on Hypericum. A great variety of polyphenolic compounds seems to be characteristic of Hypericum and related genera. Among them catechins, leucoanthocyanins including leucodelphinidin, chlorogenic acids, flavonols and condensed tannins very often occur in large amounts. The quercetin glycosides rutin, quercitrin and hyperin are very common in Hypericaceae; hyperin (= quercetin-3-galactoside) was isolated in 1938 from Hypericum perforatum and named after this plant. Most characteristic, however, are anthraquinonoid and xanthonoid pigments. They are mainly located in schizo-genous cavities which are present in roots, stems, leaves and flowers. Two photodynamically active emodin-type naphthodianthrones, hypericin and pseudohypericin, seem to occur in all members of the sections Euhypericum sensu R. KELLER, Campylosporus and Campylopus (monotypic; H. cerastoides(= rhodopeum) only), but not in other sections of the genus Hypericum. Hypericin occurs probably also in roots of Psorospermum guineense but seems to be lacking in species previously placed in Ascyrum. Celebixanthone was isolated from the bark of Cratoxylum sumatranum (= celebicum) and Haronga (= Harungana) madagascariensis contains anthra-quinones, anthrones and xanthones. Chrysophanol, physcion, madagascin, madagascinanthron, harunganin, haronginanthron and euxanthone were isolated from its bark. Very recently 2,7'-biemodyl, a new type of dimeric anthraquinones, was extracted from its leaves (). Maculaxanthone, a complex xanthone derivative has been isolated from roots of Hypericum maculatum () and uliginosin-A and -B were extracted from whole plants of the Mexican Hypericum uliginosum; both compounds are isoprenylated and acylated phloroglucin-derived phenols with strong antibiotic activity (). Eliaeaarticulata contains quercitrin, leucocyanidin and condensed tannins; anthraquinones are absent but the xanthone mangiferin is present in its leaves (). Mangiferin occurs also in leaves of Hypericum humifusum ().

Species of Hypericum do also contain essential oils stored in schizogenous cavities. A special feature of these oils is the presence of appreciable amounts of aliphatic compounds like 2-methyloctane, nonane, undecane, octanal and decanal.

Free triterpenes seem to be common in roots and barks. Friedelin and betulinic acid were isolated from the bark of Harungana madagascariensis and recently betulinic acid was shown to be a constituent of rootbark of Hypericum inodorum MILL. (= elatum AIT.) and H. andro-saemum L. (). Saponins (i.e. glycosylated triterpenes) and alkaloids seem to occur rarely in Hypericaceae.

Chemically Hypericaceae are closely related to Guttiferae. The latter produce highly characteristic pigments in their resins, oleoresins or 'latices'. The pigments are complex polyisoprenyl-ated and acylated compounds derived from phloroglucin (the so-called coumarin-type neo-flavonoids), benzophenones and xanthones. Besides, they produce biflavonoids in wood and leaves. This group of plant constituents was believed some years ago to be practically restricted to gymnosperms. Constituents like the uliginosins, euxanthone, mangiferin, celebixanthone and maculaxanthone connect Hypericaceae chemically intimately with Guttiferae.

The same is valid for the preponderance of friedelan-type and lupan-type (lupeol, betulin, betulinic acid) compounds among triterpenes and for the patterns of simple phenolics.

From the phytochemical point of view there is absolutely no need to separate Hypericaceae from Guttiferae (= Clusiaceae), i.e. to postulate family rank for Hypericoideae. — R. HEGNAUER.

Embryology

Embryo sac development in Hypericum is of the Polygonum type. Endosperm development is at first free-nuclear, and a chalazal cyst is produced at the 8- or 16-nucleate stage. This is later absorbed in the rest of the endosperm, which then becomes cellular (cf. ). Apospor-ous embryos occur in over 90 % of the seeds of H. perforatum L. (). In Triadenum the embryo sac development resembles that of Hypericum, and apospory has been reported ().