Rosaceae

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Rosaceae

Description

Leaves usually spirally arranged, sometimes distichous, rarely opposite (not in Malesia), simple or compound. Stipules on the twig or on the base of the petiole, free or adnate to petiole, rarely absent. Inflorescences various. Flowers usually bisexual and actinomorphic. Sepals usually 5, free, in some tribes an epicalyx also present. Petals usually 5, free, from large and showy to small and not or hardly distinct from sepals, in some genera/species absent. Stamens usually numerous, but sometimes the number distinctly related to the number of perianth leaves, filaments free, anthers bilocular, dehiscing longitudinally. Fruits various, fleshy or dry, dehiscent or not. Seed(s) 1 to several, without or with scanty endosperm, cotyledons fleshy or flat.

Distribution

Asia: present Asia-Tropical:, Indiapresent; New Guineapresent Australasia: South, Central, and North America: present southern hemisphere: present temperate to subtropical regions on the Northern Hemisphere: present worldwide: present
A large family with worldwide distribution, including more than 3000 species in c. 100 genera. Almost all genera which are represented in Malesia have their actual centre of distribution in temperate to subtropical regions on the Northern Hemisphere. Some of those are large or medium large genera with only one or two species in Malesia (Rosa, Alchemilla, Eriobotrya), others have a more or less distinct sub-centre in the Malesian region (Prunus, Rubus, Potentilla). Exceptional is Acaena, a genus with a Southern Hemisphere distribution, of which one species also occurs in New Guinea.
Kalkman [] postulated a Southern (Gondwanan) origin for the family and migration via three routes. Malesia in this view was reached mainly from the Asian continent (Laurasia), which in turn was reached by way of South, Central, and North America and via Beringia. Partly maybe the continent was also reached directly from Gondwana by transport on the Indian 'raft' (Alchemilla?). A third route was via Australia (Acaena). Most authors, however, favour a Laurasian origin for the family.

Ecology

As is true for almost all Malesian higher plant families, no autecological research has been carried out for members of Rosaceae. From the habitats where the species have been collected, some superficial conclusions may be drawn about preferences or tolerances for light, temperature and soil conditions and wherever possible, the paragraphs on Habitat and Ecology contain this kind of information.
Pollination is undoubtedly normally by (unspecified) insects, as in the European relatives. Apart from the formation of a good quantity of pollen and the secretion of nectar by the disc, there are no specializations in the flowers related to pollination by specific kinds of insects. Only for Acaena wind-pollination might be inferred, but experimental or observational evidence is lacking in literature or on labels.
For dispersal most Rosaceae rely heavily on animals. Exceptions are found in genera with multi-seeded follicles with dry seeds (in Malesia only Neillia) where dispersal is by ballistochory. The same is true for most of the Potentilla species that have the dry achenes in the cups formed by the hypanthium, sepals and epicalyx. Some genera have dry achenes, imbedded in or surrounded by a fleshy spurious fruit (Rosa and also the not indigenous Fragaria and Potentilla indica). In these cases the hypanthium, resp. the torus functions as the attractant for endozoochory by snails, birds, or other animals. Many Rosaceae of different tribes have gone the way to fruits with a fleshy or juicy layer in their walls (drupes, either single or as collective, or pomes) and obviously these are also endozoochorous. Epizoochory is only exercised by Acaena and Agrimonia which possess spines on their hypanthium in which the fruit is included.

Morphology

As apparent from the family description, there is variation in many characters of leaves, flowers, and fruits. The presence of a well-developed hypanthium, a probably axial outgrowth from the top of the pedicel surrounding the pistil(s), is about the only character that is common to all Rosaceae. The elaboration of this hypanthium causes much of the variation in flowers and fruits. The plesiomorphic (original) situation is still present in Spiraeoid genera that have a small number (up to 5) multi-ovulate ovaries on the bottom of a cupular hypanthium, the ovaries developing into ventrally dehiscent, dry-walled follicles containing several seeds.

Adnation of the ovaries to the inside of the hypanthium, accompanied by a more or less complete fusion of the ovaries with each other, creates the possibility for the evolution of the fleshy, (semi-)inferior fruits that are typical for Maloideae. In this group the exc carp of the inferior fruit is certainly hypanthial, the endocarp (membranous to woody) is certainly carpellary, the more or less fleshy mesocarp may be either or both. In the descriptions in this treatment the terms exocarp, mesocarp, and endocarp are used in their topographical sense, for superior as well as inferior fruits and thus not implying a carpellary origin.

Another line of evolution is the change of dry, multi-seeded follicles into dry, 1-seeded achenes, that later may develop a fleshy fruitwall and become drupaceous. Examples are manifold in Rosoideae (e. g. Rubus with many pistils per flower) and all Prunoideae have drupes too, with one pistil per flower.

Anatomy

Although many papers have been published on the leaf anatomy of the Rosaceae, litde is known of the anatomy of the tropical representatives, especially of the Malesian species. The situation for wood anatomy is much better with recent comprehensive studies by Zhang (1992), Zhang & Baas (1992) and Zhang et al. (1992). The following is a concise summary for the Malesian representatives (wild and cultivated) of data surveyed more extensively in Metcalfe & Chalk (1950) and the above-mentioned wood anatomical studies, amplified with scattered data from the other papers cited below.

Leaf anatomy. Trichomes if present usually unicellular, but tufted or stellate hairs occur in Potentilla p.p. and Rubus p.p.; stalked capitate glands have been recorded in Alchemilla, Fragaria, Potentilla, Prunus, Rosa, Rubus, and Sanguisorba. Epidermal cells of lower epidermis sometimes papillate.

Extrafloral nectaries present on the petiole and various parts of the leaf blade of Prunus p.p.; leaf teeth glandular or hydathodal in species of Alchemilla, Fragaria, Prunus, Pyrus, Rubus, Sanguisorba, and Spiraea. Stomata almost always confined to the lower leaf surface, usually anomocytic, but cyclocytic, staurocytic, tetracytic, and actinocytic types may also occur (Lu et al. 1991). Upper epidermal cells often (partly) mucilaginous. A hypoder-mis is differentiated in some species of Prunus ('Pygeum') and Rubus (section Micrantho-batus). Mesophyll dorsiventral. Vascular bundles of minor veins with or without scleren-chyma in bundle sheath, only rarely vertically transcurrent. Vascular system of midrib and petiole ranging from a single collateral bundle to more complex, open or closed systems. Nodes usually trilacunar, but 5-, 7-, and 9-lacunar nodes recorded in Rubus (Kato 1966, 1967). Crystals solitary and/or clustered. Tanniferous cells common. Mucilage idioblasts present in the mesophyll of some species.

Uses

The usefulness of the Rosaceae is mainly to be found in the presence of many edible, and often delicious fruits. See: Eriobotrya, Fragaria, Malus, Prunus, Rubus, Pyrus.
Timber hardly enters the world market, but may well be useful on the local scale.
Medicinal uses appear to be scarce in the region judged from label data and Malesian literature. These sources may not give a complete picture considering the extensive use made of Rosaceous species in traditional medicine in East Asia (see also the chapter on phytochemistry, p. 233).

Citation

Vidal - in Fl. Thailand. 1970
Hutch. - in Gen. Flow. Pl. 1964
Tirvengadum - in Fl. Ceylon. 1981
Vidal - in Fl. Camb., Laos & Vietnam. 1968
Nguyen Van Thuan - in Fl. Camb., Laos & Vietnam. 1968