THE SYSTEMATICS AND ANATOMY OF GONGYLOCARPUS (ONAGRACEAE)

The unique fruiting structures of the closely related, principally Mexican, monotypic genera Gongylocarpws and Burragea (Onagraceae) compelled a detailed anatomical and cytological investigation of these plants which led to the conclusion that they should be included in a single genus, Gongylocarpus. Gongylocarpus fruticulosus (Burragea), endemic to two adjacent islands off the west coast of Baja California, is divided into two subspecies, subsp. fruticulosus and subsp. glaber. The vegetative and floral anatomy, including wood anatomy, of both species is described. The fruits of these two species grow into the stem by meristematic activity during the course of ontogeny, the ovaries in the mature flower being superficial and sessile in the leaf axil. There is no pedicel associated with the flower, but only a branch gap. Meristematic tissue at the base of the locules divides rapidly at a relatively late ontogenetic stage, the ovaries growing downward into the stem and crushing the pith. The mature, heavily sclerenchymatous fruits are located wholly within the stem, and in G. fruticulosu.s they are aggregated into long chains. Both species have a gametic chromosome number of n = 11, a characteristic otherwise unknown in the tribe Onagreae but shared with other generalized groups in the family. Taken together with other features, this suggests a primitive position within the tribe for Gongylocarpus. GONGYL0CARPuS (0NAGRAcEAR) is a principally Mexican genus of two very distinctive species characterized by a unique fruiting structure. In both, as will be shown in this article, the mature capsules become deeply imbedded in the pith of the stems on which they are borne. One of these species, G. rubricaulis Schlecht. & Cham. (Fig. 3), is a weedy annual with small white flowers, widespread in mainland Mexico and adjacent Guatemala, from ca. 1200—2300 m elevation (Fig. 1). The other, G. fruticulosus (Benth.) T. S. Brandegee (Fig. 2), is a low shrub with large purple flowers, entirely confined to two adjacent islands in Bahia Magdalena, Baja California, where it occurs near sea level (Fig. 1). The latter was segregated as the genus Bur ragea by Smith and Rose in 1913, and this segre gate genus has subsequently been accepted as distinct. The present study was undertaken to determine the degree of relationship between these two habitally very distinct species, particu larly in the light of a comparative anatomical investigation; to investigate their position within the family Onagraceae; and to provide an ade quate description of the ontogeny of their bizarre fruiting structures. ‘Received for publication May 25, 1965. This work was supported in part by National Science Foundation grants GB—14 and GB—4161 (Raven). The authors are grateful to Dr. Reid Moran for his excellent anatomical and cytological material of Gongylocarpus fruticulosus (Burragea), and especially to Mr. and Mrs. Richard Dwyer, owners of the research vessel Gringa, for making Dr. Moran’s trip possible; and to Mr. D. E. Breedlove (supported in the field by N.S.F. grant GS—383) for his fine material and observations of C. rubricaulis. The genus Gongylocarpus first came to the attention of the botanical world through collec tions of the weedy annual G. rubricaulis (Fig. 3) made by Schiede and Deppe from “eultis et incultis circa Jalapam” (i. e., near Jalapa, Vera Cruz). This material was made the basis of a new genus and species by Schlechtendal and Chamisso in 1830. The species is so distinct and uniform that it has never been placed in any other genus, described under any other name, or subdivided taxonomically. Its flowers open early in the morning and the short white petals are fugacious; collections made in the middle of the day or in the afternoon often lack them com pletely. The anthers deposit pollen directly on the globose stigma soon after the flowers open, although the stigma may ultimately be held above the anthers. A full complement of seed is set following self-pollination. We have not seen insects at the flowers of the two populations studied in Chiapas (cited below), nor on plants cultivated in San Cristobal las Casas, Chiapas, within the native range. This predominant autog amy may help to account for its uniformity over its rather wide range (Fig. 1). Gongylocarpus rubricaulis very often occurs as a weed in corn fields, where its lax reddish stems may be con spicuous locally; sometimes it is found on rocky slopes, particularly in disturbed ground, and sometimes in moist places. Although widespread, it is not often collected and is rather sporadic and local in occurrence. The second species of the genus, G. fruticulosus (Fig. 2), was described by Bentham (1844, p. 15) as an aberrant species of Gaura. Bentham