JOURNAL OF THE ARNOLD ARBORETUMVOL. XXXV JANUARY 1954 NUMBER 1 STUDIES IN THE BORAGINACEAE, XXVI FURTHER REVALUATIONS OF THE GENERA OF THE LITHOSPERMEAE IVAN M. JOHNSTON PREPARATORY TO A GENERAL DISCUSSION of the Lithospermeae to bepublished in the near future, seventeen genera of the tribe are given indi-vidual treatment in the present paper. These, along with six genera dis-cussed previously, Jour. Arnold Arb. 34: 258-299 (1953), include all thegenera which can be referred to the tribe if that is to be a homogeneousdivision of the Boraginoideae. Of the seventeen genera here discussed onlyone, Lithospermum, has representatives native to both America and the OldWorld or has direct relations with genera in both regions. Since the dis-tribution and relationships of all other genera are confined within one orthe other of these major regions, the primary division in my key to thegenera has been deliberately based on geography. For most uses this willbe a convenience. Furthermore, it also has the advantage of permittingsharper contrasts of immediately related genera. A synopsis of all the generaof the tribe and technical keys for their identification will be provided inthe following paper of this series. KEY TO THE GENERAPLANTS NATIVE TO AMERICA.Anthers completely exserted from the throat; filaments elongate, 6-70 mm. long, exserted 1-65 mm. from the corolla mouth; corolla large, 39-90 mm. long, trumpet-shaped, lobes usually ascending or recurved or reflexed; pollen ellipsoidal to ovoid or ovoid-oblong, 23-33 X 15-28 . . .. 1. Macromeria.Anthers completely included in the throat or only partially exserted from the corolla mouth; filaments at most 10 mm. long and usually very much shorter, completely included or exserted less than 1 mm.; corolla smaller, usually less than 25 mm. long and never more than 50 mm. in total length, tubular to salverform, lobes erect to spreading. Flowers precociously sexual, corolla opening and exposing stamens and style before attaining full size; corolla-lobes erect, sharply acute or acute with an attenuate tip, very narrowly imbricate in the bud, usually evidently longer than broad; sinus between the corolla-lobes plicate and inflexed and thickened at the base; pollen ovoid, 16-24 X 13-22 p�....2. Onosmodium.