272 AMMIACEAE. 



teeth seldom conspicuous. Petals 5, usually with an inflexed tip, often 

 emarginate or 2-lobcd, those of the outer flowers sometimes larger than 

 those of the inner. Stamens 5, inserted on the epigynous disk; filaments 

 filiform ; anthers versatile. Ovary inferior, 2-celled ; styles 2, filiform, per- 

 sistent, often borne on a conic or depressed stylopodiurn ; ovules 1 in each 

 cavity, pendulous, anatropous. Fruit dry, composed of 2 carpels (meri- 

 carps), which generally separate from each other at maturity along the 

 plane of their contiguous faces (the commissure). Fruit either flattened 

 laterally (at right angles to the commissure), or dorsally (parallel to the 

 commissure), or nearly terete (not flattened). Carpels after parting from 

 each other supported on the summit of a slender axis (the carpophore), 

 each with 5 primary ribs in their pericarps (rarely ribless), and in some 

 g-enera with 4 additional secondary ones, the ribs or some of them often 

 winged. Pericarp usually containing oil-tubes between the ribs, or under 

 the ribs and on the commissural sides, sometimes irregularly scattered, some- 

 times none. Seeds 1 in each carpel ; seed-coat thin ; endosperm cartilag- 

 inous; embryo small, placed near the hilum. About 250 genera and prob- 

 ably 2000 species, of wide distribution. The mature fruit is necessary for 

 the certain determination of most of the genera and many of the species. 



Leaves simple. 



Ribs of the fruit not anastomosing. 1. Hyrtroroti/li'. 



Ribs of the fruit anastomosing. 2. Ccntellu. 



Leaves compound or decompound. 



Fruit with both primary and secondary ribs, the latter armed 



with hooked prickles. 3. Torilix. . 



Fruit with primary ribs only. 



Flowers yellow or greenish-yellow. 



Involucre of 2-4 linear bracts. 4. Apium. 



Involucre none. 



Fruit terete or nearly so; leaf-segments filiform. 5. Foenicitlitm. 

 Fruit flattened; leaf-segments broad. 6. SniyrniitiH. 



Flowers white. 



Umbels terminal. 7. Amml. 



Umbels, at least the lower, opposite the leaves. 



Perennials ; leaf-segments broad. 8. Celcri. 



Annuals ; leaf-segments filiform. 0. Helosciadium. 



1. HYDBpCOTYLE L 



Perennial herbs, prostrate and commonly rooting at the joints, with 

 palmately lobed or veined, often peltate leaves, the bases of the petioles with 

 2 scale-like stipules, and small white flowers in umbels opposite the leaves. 

 Bracts of the involucre few, or none. Calyx-teeth minute. Petals entire. Disk 

 flat. Fruit laterally compressed, orbicular or broader than high. Carpels with 

 5 primary ribs, the lateral ones usually curved ; no large oil-tubes, but an oil- 

 bearing layer of tissue beneath the epidermis. [Greek, water-cup.] About 

 75 species of wide distribution. Type species: Hydrocotyle vulgaris L. 



