1960] WILSON, HYDROPHYLLACEAE AND POLEMONIACEAETHE GENERA OF IIYDROPHYLLACEAE AND POLEMONIACEAE IN THE SOI TITEASTERN UNITED STATES I KENNETH A. WILSON HYDROPHYLLACEAE R. Brown ex Edwards (\WATERLEAF FAMILY) Annual, biennial or perennial herbs or rarely shrubs] with alternateor opposite, entire, pinnately or palmately divided leaves. Inflorescencesterminal, axillary, or opposite the leaves, the flowers in cymes, panicles,or solitary. Flowers bisexual, regular, 5-merous. Calyx 5-parted, thesinuses sometimes bearing appendages. Corolla rotate, campanulate orfunnelform, 5-parted. Stamens 5, epipetalous. Gynoecium syncarpous:styles 2 (rarely more) or 1, terminal: ovary superior. 1-locular with 2parietal placentae or 2-locular and the placentation axile. Ovules 4-many,anatropous or amphitropous. Fruit a capsule. A family of about 18 genera and 250 species in three tribes, primarilyof North America, but extending into South America, Asia, and Africa.The family is represented in the United States by 15 genera centered inthe Southwest; six genera occur in our area. The family is regarded as being closely allied to the Polemoniaceaeand the Boraginaceae. It may be distinguished from them by the combina-tion of bicarpellary 1-or 2-locular ovary (usually with numerous ovules)and the usually imbricate aestivation of the flowers which are generallyborne on scorpioid cymes. Considerable variation is evident in the struc-ture and nature of the ovary. The gynoecium is 2-carpellate; the placen-tae may be parietal and fleshy or they may be narrow, extending intothe ovary to meet without fusing and partition the ovary into twolocules. In Hydrolca further elaboration of the placentae, accompaniedby a fusion of the dividing wall, has produced a 2-locular ovary withaxile placentation. The Hydrophyllaceae are cytologically perhaps the best known familyof any size. Information on the chromosome numbers of the species in 'Prepared for a biologically oriented generic flora of the southeastern United States, a joint project of the Gray Herbarium and the Arnold Arboretum made pos-sible through the support of George R. Cooley and the National Science Foundation, and under the direction of Reed C. Rollins and Carroll E. Wood, Jr. The scheme follows that outlined at the beginning of the series (Jour. Arnold Arb. 39: 296-346. 1958). Other published portions of these studies will be found in Jour. Arnold Arb. 40, 41. 1959, 1960. I am grateful to Lincoln Constance who has offered many help-ful suggestions and comments in connection with the Hydrophyllaceae. I wish also to express my indebtedness to R. B. Channell, G. R. Cooley, and H. F. L. Rock for their assistance in supplying information, aiding in the obtaining of specimens, and helping in various ways.