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(Last Modified On 11/13/2012)
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(Last Modified On 11/13/2012)
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Family
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ROSACEAE
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Contributor
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ROGERS McVAUGH
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Description
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Herbs, shrubs or trees with leaves alternate, rarely opposite, simple or com- pound, usually with conspicuous stipules. Flowers usually perfect and regular, the perianth perigynous, the axis sometimes enlarged to form a flat or concave recep- tacle or hypanthium bearing the calyx-lobes, petals, and stamens on its margin, and usually lined inside with a glandular disk; calyx-lobes 5 (sometimes 4), imbri- cate; petals usually 5 and imbricate, sometimes wanting; stamens few to many, often about 20; carpels 1 to many, distinct or united, often connate with the receptacle; styles as many as the carpels, sometimes connate. Fruit various; seeds usually without appreciable endosperm, the cotyledons often fleshy and convex, rarely folded or convolute.
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Habit
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Herbs shrubs
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Habit
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trees
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Note
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The Rosaceae comprise approximately 100 genera, well represented in almost all parts of the world. They include many plants of economic importance, especially in temperate regions where they are much cultivated for food and orna- ment (e. g., the genera Fragaria, Rubus, Rosa, Spiraea, Prunus, Pyrus, Malus, Chaenomeles, Rhodotypus, etc.). Some workers have advocated the division of the family into several segregate families, on the basis of characters of the fruit; thus genera with the fruit an achene or a follicle have been made to constitute the Rosaceae proper, genera with drupaceous fruit the Amygdalaceae, and genera with pomaceous fruit the Malaceae. These segregations appear unjustified because of the very large number of characters of the flowers, inflorescences and vegetative parts which are repeated in genus after genus without regard to fruit type, and which together make of the inclusive Rosaceae an easily comprehensible and evi- dently natural group of related genera. Precise determination of specific limits is difficult in many genera, related groups often seeming to merge morphologically or to differ by minor characters only. Apparently much of the difficulty arises from the frequent occurrence in the family of reproductive methods other than a sexual fusion of haploid gametes followed by regular reduction-division. Several genera are known to include species in which polyploidy, aneuploidy, apomixis and other irregularities have been demonstrated, and it may be supposed that these phenomena have contributed largely to the formation of the numerous minor geographic races which are known to exist, in nature isolated in small disjunct areas or if growing with other related species then barely distinguishable from them.
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Key
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a. Leaves pinnately or palmately compound, with 3 or more leaflets. b. Upright or trailing shrubs with prickly canes and leaves (brambles); petals present and conspicuous; fruit of few or numerous drupelets borne on an enlarged receptacle- - 3. RUBUS bb. Herbaceous or low suffrutescent plants with unarmed leaves and stems; corolla wanting. c. Hypanthium covered with barbed spines, in fruit forming a bur; erect plants up to 1 m. tall, the inflorescence spicate or racemose.. 5. ACAENA cc. Hypanthium unarmed; flowers very small (rarely as much as 3 mm. long); plants mostly prostrate or procumbent, the inflorescence cymose, often corymbiform- - .--..---------- 4. ALCHEMILLA aa. Leaves simple. b. Herbaceous, usually prostrate plants with lobed leaves; flowers very small (rarely as much as 3 mm. long); corolla wanting; calyx-lobes alternating with bracts, the lobes apparently 8-10 in number; hypanthium at maturity containing a few achenes -4. ALCHEMILLA bb. Shrubs or trees with simple unlobed leaves; flowers larger; corolla usually present; calyx-lobes usually 5, without alternating bractlets; fruit dry or fleshy. c. Styles 5, distinct; fruit of 5 thin-walled achenes, or of 5 bony nutlets in a fleshy hypanthium (pome); leaves dentate. d. Fruit of 5 achenes about 2 mm. long; unarmed shrubs with leaves white-tomentose beneath, and flowers in ample panicles 5-15 cm. long ......................... 1. HOLODISCUS dd. Fruit a pome up to 1 cm. long, red or black; spinescent shrubs, nearly glabrous or the branchlets rufous-pubescent, the flowers in corymbose cymes 2-3 cm. long .. -.-...... 2. HESPEROMELES cc. Style 1; fruit a dry or fleshy drupe with- a single large stone; leaves entire. d. Style terminal on the ovary or essentially so; stamens usually 20; flowers (in Panamanian species) in glabrous simple axillary racemes which are ebracteate at flowering time .............................. 6. PRUNUS dd. Style arising from the base of the ovary; stamens usually 15 or fewer; flowers in cymes or panicles, if in simple racemes these bracteate and pubescent. e. Filaments 10-16 mm. long; stamens 3-7 .................................... 9. HIRTELLA ee. Filaments 1-6 mm. long; stamens 15-20 (-30?) or if only about 3 anther-bearing, then less than 1 mm. long. f. Hypanthium 5-6 mm. long (excluding the calyx-lobes) in bud, elongate, somewhat gibbous, the ovary attached lateral- ly somewhat above the base of the hypanthium-cavity 10. COUEPIA ff. Hypanthium 3 mm. long or less in bud and in anthesis, cup-shaped or campanulate, symmetrical, the ovary attached at the base of the internal cavity. g. Flowers 8-20, in nearly sessile axillary cymes (2-4 cm. long) shorter than the leaves; low shrub, or medium- sized tree up to 5-6 m. tall -......................- .7. CHRYSOBALANUS gg. Flowers very numerous, in axillary and terminal panicles 10-40 cm. long, with divaricate leafless branches; trees, often 10-15 m. tall or more . -.-.. 8. LICANIA
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Note
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A weedy immigrant from the United States, Potentilla norvegica L., was re- ported from San Jose Island by Johnston (Sargentia 8:31, 132. 1949). It is not to be expected that this species will maintain itself permanently in competition with the native flora. It is a hirsute herbaceous annual or biennial with 3-foliolate leaves, leafy cymes, and conspicuous yellow flowers.
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