Cauline leaves mostly in 5-8 pairs, blade ± ascending throughout, 0.8-1.2 mm wide. Inflorescences: branches erect to ascending. Flowers: sepals 4.5-7.2 mm, to 8 mm in fruit, ± glabrous; nectaries thickened, molarlike, apically 2-lobed, 1-1.5 mm. Flowering spring-summer. Open woodlands, sagebrush flats, dry, rocky slopes, alluvial deposits, often on carbonates; 600-2200 m; Ariz., Calif., Nev., Utah. Plants with petals equaling or barely exceeding the sepals and with cauline leaves fewer than five pairs have been recognized as Arenaria macradenia var. parishiorum; those features intergrade completely with var. macradenia. See M. F. Baad (1969) for his reasons for accepting var. parishiorum as a species.

B. Maguire (1947) included 'Lower California' in his distribution statement for var. macradenia, implying Baja California; we have not seen any collections from that area.