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The families of flowering plants.                                                                                                                                                                

Oxalidaceae R. Br.

                        

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ExcludingAverrhoaceae, Hypseocharitaceae, Lepidobotryaceae

Habit and leaf form. Herbs. Switch-plants (sometimes), or ‘normal’ plants (mostly); occasionally phyllodineous. Leaves well developed (usually), or much reduced. Plants succulent (sometimes), or non-succulent (mostly). Perennial; with a basal aggregation of leaves, or with neither basal nor terminal aggregations of leaves; rhizomatous, or tuberous. Hydrophytic to helophytic, or mesophytic, or xerophytic; when hydrophytic, rooted. Leaves alternate; spiral; ‘herbaceous’ (mostly), or fleshy (in CAM species, e.g. Oxalis megalorrhiza); petiolate; non-sheathing; compound; unifoliolate, or ternate, or pinnate, or palmate. Leaflets often pulvinate (exhibiting ‘sleep movements’). Lamina pinnately veined. Leaves exstipulate; without a persistent basal meristem. Vernation circinnate (usually), or not circinnate (?).

Leaf anatomy. Hydathodes present (sometimes), or absent.

Lamina with secretory cavities (commonly), or without secretory cavities. Minor leaf veins without phloem transfer cells (Oxalis).

Stem anatomy. Cork cambium present, or absent (?); initially superficial. Nodes tri-lacunar. Secondary thickening absent, or developing from a conventional cambial ring (?). Xylem with libriform fibres; with vessels. Vessel end-walls simple. Sieve-tube plastids P-type (Oxalis), or S-type (Biophytum).

Reproductive type, pollination. Fertile flowershermaphrodite. Plants hermaphrodite (often with additional small cleistogamous flowers); usually heterostylous (mostly tristylous).

Inflorescence, floral, fruit and seed morphology. Flowers solitary, or aggregated in ‘inflorescences’; in cymes, in panicles, and in umbels. The ultimate inflorescence unit cymose. Inflorescences axillary; cymes or ‘sub-umbellate’, often pedunculate. Flowers small to large; regular; 5 merous; cyclic; tetracyclic to pentacyclic. Free hypanthium absent. Hypogynous disk present, or absent.

Perianth of chasmogamous flowers with distinct calyx and corolla; 10; 2 whorled; isomerous. Calyx 5; 1 whorled; polysepalous; regular; persistent; imbricate. Corolla 5 (often lacking in cleistogamous flowers); 1 whorled; polypetalous (usually), or gamopetalous (sometimes slightly connate basally). Corolla lobes markedly longer than the tube. Corolla contorted (usually), or imbricate; regular. Petals sometimes shortly clawed, or sessile.

Androecium10. Androecial members free of the perianth; all equal, or markedly unequal (the outer whorl usually with shorter filaments); coherent; 1 adelphous (the filaments basally connate); 2 whorled. Androecium exclusively of fertile stamens, or including staminodes. Staminodes when present, 5; external to the fertile stamens. Stamens 5, or 10; diplostemonous, or isomerous with the perianth; alternisepalous (the shorter, outer members opposite the petals), or oppositisepalous (when the outer members lack anthers); alternating with the corolla members, or both alternating with and opposite the corolla members. Anthers dorsifixed; dehiscing via longitudinal slits; introrse; tetrasporangiate. Endothecium developing fibrous thickenings. Microsporogenesis simultaneous. The initial microspore tetrads tetrahedral, or decussate. Anther wall initially with one middle layer, or initially with more than one middle layer (1 or 2). Tapetum glandular. Pollen grains aperturate; 3(–4) aperturate; colpate (to colporoidate?, occasionally 4-rupate); 2-celled (in Oxalis).

Gynoecium 5 carpelled. Carpels isomerous with the perianth. The pistil when syncarpous, 5 celled. Gynoecium apocarpous to syncarpous; semicarpous to synovarious (the carpels more or less free in Eichleria, Biophytum);superior. Carpel (when semicarpous), capitate stylate. Placentation when carpels more or less free, marginal. Ovary usually syncarpous and 5 locular (the lobes opposite the petals). Styles 5; free. Stigmas dry type; papillate; Group II type. Placentation nearly always (i.e. when syncarpous) axile. Ovules 2–15 per locule (to ‘several’); pendulous; epitropous; with ventral raphe; arillate (often); anatropous, or hemianatropous; bitegmic; tenuinucellate. Outer integument contributing to the micropyle. Embryo-sac development Polygonum-type. Polar nuclei fusing only after one has been fertilized, or fusing simultaneously with the male gamete. Antipodal cells formed; 3; not proliferating; ephemeral. Synergids pear-shaped, or hooked. Endosperm formation nuclear. Embryogeny asterad.

Fruit non-fleshy; when semi to apocarpous, an aggregate (e.g. Biophytum), or not an aggregate (usually); when syncarpous (i.e. usually) dehiscent; a capsule. Capsules loculicidal. Fruit often elastically dehiscent (involving the arilliform epidermis of the seeds). Seeds usually copiously endospermic. Endosperm ruminate; oily. Cotyledons 2. Embryo chlorophyllous (1/3); straight.

Seedling.Germination phanerocotylar.

Physiology, biochemistry. Not cyanogenic. Alkaloids absent (3 species). Iridoids not detected. Proanthocyanidins present, or absent; when present, cyanidin, or cyanidin and delphinidin. Flavonols mostly absent. Ellagic acid absent (6 Oxalis species). Saponins/sapogenins present, or absent. Aluminium accumulation not found. Plants accumulating free oxalates. C3 and CAM. C3 physiology recorded directly in Oxalis stricta. CAM recorded directly inOxalis carnosa. Anatomy non-C4 type (Oxalis).

Geography, cytology. Temperate to tropical. Cosmopolitan except for frigid regions, concentrated in the tropics and subtropics. X = (5-)7(-12).

Taxonomy.Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Rutiflorae; Geraniales. Cronquist’s Subclass Rosidae; Geraniales. APG 3 core angiosperms; core eudicot; Superorder Rosanae; fabid; Order Oxalidales.

Species 875. Genera 3; Oxalis, Biophytum, Eichleria.

 Illustrations:

  • Technical details: Oxalis.
  • Technical details: Oxalis (Lindley).
  • Technical details : Biophytum (Thonner).
  • Oxalis acetosella, Oxalis corniculata and Oxalis stricta: Eng. Bot. 310–312, 1864.
  • Oxalis acetosella (B. Ent.).
  • Oxalis fruticosa (phyllodineous): Bot. Reg. 41, 1841.
  • Oxalis hirta: Bot. Reg. 1073, 1827.
  • Oxalis piottae, cf. O. punctata: Bot. Reg. 1817, 1836. 
  • Oxalis rubrocincta: Bot. Reg. 64, 1842. 
  • Oxalis tortuosa: Bot. Reg. 1249, 1829.
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