Citation: L., Sp. Pl. 385 (1753).

Derivation: Greek zygon, yoke, pair; phyllon, leaf; referring to the pair of leaflets which compose each leaf.

Synonymy: Not Applicable

Common name: Squashes, twinleaves.

Description:
Annual herbs or perennial subshrubs with fleshy branches and leaves, glabrous or almost so; leaves opposite, paripinnate, with 2 leaflets (in Australian species) or simple, linear or 2-lobed when leaflets are continuous with the flattened cuneate petiole.

Flowers solitary, axillary, usually pedunculate; sepals 4 or 5, imbricate, with green centre and membranous margins; petals 3-5, imbricate, clawed, yellow, white or orange, rarely red; stamens 4, 6, 8 or 10; disk between stamens and ovary sinuate or distinctly 3-5-lobed or 3-5-partite, the lobes at the base of the septa which separate the cells of the ovary; ovary 3-5-celled, 3-5-angular; style subulate; stigma capitate or lobed.

fruit an angular loculicidal capsule, or vertically winged and indehiscent, or breaking into 2-4 cocci; seeds with endosperm, 1-6 in each cell, mucous when wet.

Distribution:  About 120 species, in Australia about 20 species, all endemic, from the Mediterranean to Central Asia, South Africa and Australia; in deserts and steppes.

Biology: Some species contain high levels of nitrate and have been suspected of causing sudden death of cattle.

Taxonomic notes: The genus, as treated in Australian handbooks, is heterogeneous, and some species may have to be excluded.

Key to Species:

1. Fruit 3- or 4-winged, indehiscent or septicidally breaking into up to 4 cocci; filaments without wings or appendages in the lower part. 2. Fruit 3-winged; stamens 6; leaves sessile, cuneate, with 2 short broad obtuse lobes at the apex, upper pairs connate at the base; annual	Z. howittii 10.
2. Fruit 4-winged; stamens 8; leaves petiolate or, if sessile, distinctly separate; mostly perennial
3. Petals obovate, obtuse or faintly notched at the apex, golden-yellow; fruit 12-18 mm diam., splitting into 2-4 cocci when ripe; seeds usually 1 (rarely 2) in each coccus	Z. aurantiacum 3.
3. Petals narrow-oblanceolate, almost acute at the apex, a pale lemon-yellow; fruit 8-12 mm diam., not splitting into cocci; seeds usually only 1 in each fruit	Z. eremaeum 8.
1. Fruit angular, loculicidal; filaments sometimes winged or with appendages in the lower part
4. Capsule 5-celled, 5-angled; flowers 5-merous; stamens 10
5. Capsule truncate at the apex, with a short blunt appendage at the upper corner of each angle; seed 1 in each cell	Z. apiculatum 2.
5. Capsule rounded at the apex, without appendages at the angles
6. Capsule ovoid-oblong, 10-12 mm long; seeds 3-6 in each cell;petals yellow
7. Fruiting peduncles erect; leaflets entire at the apex, usually broadened with a broad lobe at the outer side at the base	Z. hybridum 12.
7. Fruiting peduncles deflexed; leaflets usually with 3 blunt teeth at the apex, without a basal lobe	Z. kochii 14.
6. Capsule more or less globular, 5-7 mm long; seeds 1 or 2 in each cell; leaflets rounded or emarginate at the apex
8. Petals yellow, scarcely exceeding the sepals; fruiting peduncles 3-4 mm; seeds glossy	Z. iodocarpum 13.
8. Petals white, about twice as long as the sepals; fruiting peduncles 7-15 mm long; seeds dull	Z. tesquorum 17.
4. Capsule 4-celled, 4-angled; flowers 4-merous; stamens 8 or 4
9. Capsule almost sessile, erect, narrow-cylindrical to narrow-ellipsoidal, with 4 erect thick appendages at the apex	Z. prismatothecum 16.
9. Capsule distinctly pedicellate, drooping, broader, without apical appendages
10. Leaflets crenate at the apex (i.e. usually with 3 blunt teeth)	Z. crenatum 7.
10. Leaflets entire or notched at the apex
11. Capsule truncate at the apex
12. Perennial; capsule 8-12 mm long; petals yellow	Z. billardierei 4.
12. Annual; capsule 5-7 mm long; petals white or yellow	Z. ammophilum 1.
11. Capsule rounded at the apex
13. Petals white, usually shorter than the sepals; capsule ellipsoidal, c. 8 mm long; leaflets narrow-oblong- cuneate, faintly notched; seeds usually 2 in each cell	Z. ovatum 15.
13. Petals yellow, longer than the sepals
14. Capsule subglobular, 3-4 mm long; seed 1 in each cell; leaflets notched at the apex	Z. humillimum 11.
14. Capsule larger, 7 or more mm long; usually several seeds in each cell; leaflets entire, with a rounded or acute apex
15. Leaflets more or less appressed to each other with their upper surfaces, ovate, 8-15 mm long, the uppermost oblong with an acutish apex; disk-lobes linear-oblong, truncate, almost as long as the ovary; capsule obovoid, 7-10 mm long; petals 4-6 mm long	Z. compressum 5.
15. Leaflets divergent in the same plane, oblique-obovate, 1-4 cm long, the uppermost rounded at the apex; disk-lobes broader than long, rounded, much shorter than the ovary
16. Capsule ovoid-oblong to obovoid-oblong; seeds 3-5 in each cell; petals 8-15 mm long; leaflets usually articulate at the base; petals 8-15 mm long	Z. glaucum 9.
16. Capsule very broad, oblong to almost globular; seeds 1 or 2 in each cell; petals 6-7 (rarely to 9) mm long; leaflets appearing continuous with the petiole (no articulation visible when fresh); very fleshy thick-stemmed glaucous subshrub of dry northern parts of S.Aust	Z. crassissimum 6.

Author: Not yet available