370 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



9. ACACIA Willd. Sp. PI. 4: 1049. 1806. 



Refebence : Benth. Trans. Linn. Soc. Bot. 30: 444-533. 1875. 



Trees or shrubs, rarely herbs, usually armed with spines; leaves bipinnate, 

 the leaflets usually small and numerous, the petiole usually glanduliferous ; 

 flowers small but often showy, capitate or spicate, the stamens numerous 

 (sometimes as many as 400), exserted; fruit very variable in form. 



The species of Acacia are widely distributed in the tropics of both hemis- 

 pheres, being particularly abundant in Australia. Many of them yield useful 

 gums, gum arable being furnished by A. scorpioides (L.) W. F. Wight [A. 

 arabica (Lam.) Willd.] and other species. This gum is employed in medicine 

 as a remulcent and has varied uses in different industries. 



A. Spines very large, most of them 5 mm. wide at the base or often much 

 broader, either inflated and then usually punctured by ants or flattened 

 and sword-shaped, never abruptly recurved, sometimes boat-shaped. 

 Involucel borne at or above the middle of the peduncle; bractlets of the 

 flower heads not peltate; spines often puberulent when young. 

 Flowers in globose heads. 



Spines boat-shaped 1. A. cochliacantha. 



Spines sword-shaped, flat 2. A. macracantha. 



Flowers in cylindrical spikes. 



Spines turgid and only slightly compressed 3. A. standleyi. 



Spines flat, strongly compressed 4. A. gladiata. 



Involucel borne near the base of the peduncle, or at least below the middle; 

 bractlets peltate ; spines glabrous. 

 Fruit indehiscent, terete, terminating in a spinose beak. 



Flowers in globose or oblong-globose heads 5. A. sphaerocephala. 



Flowers in long cylindric spikes 6. A. cornigera. 



Fruit dehiscent. 



Fruit opening by a single suture. Flowers spicate 7. A. hindsii. 



Fruit opening by 2 sutures. 



Flowers in globose heads 8. A. globulifera. 



Flowers in cylindric spikes. 



Spines much broadened and compressed at base ; fruit somewhat 



compressed 9. A. nelsonii. 



Spines little broadened and scarcely at all compressed; fruit terete 



or nearly so 10. A, collinsii. 



AA. Spines often wanting, when present much smaller, usually much less than 

 5 mm. wide at base, never boat-shaped or large and sword-shaped, often 

 abruptly recurved. 

 B. Flowers spicate. 



Leaflets large, all or most of them more than 1 cm. wide. 



Flowers pedicellate. Plant glabrous 11. A. reniformis. 



Flowers sessile. 



Stipular spines mostly 1 to 3 cm. long 13. A. conzattii. 



Stipular spines 5 mm. long or shorter. 



Leaves densely short-pilose at maturity 15. A. calif ornica. 



Leaves glabrous or nearly so at maturity or puberulent. 



Fruit 5 mm. wide or narrower 14. A. pringlei. 



Fruit 1 to 2.5 cm. wide. 

 Pinnae one pair; leaflets subchartaceous, longer than broad. 



16. A. unijuga- 

 Pinnae 2 or 3 pairs ; leaflets coriaceous, nearly as broad as long. 



12. A. sororia. 



