Between Arenaria leptoclados on the one side and A. serpyllifolia s.s. (including subsp. macrocarpa) on the other a difference exists in the structure of the mature, dry capsules. In A. leptoclados these usually have a dented or pleated appearance. When compressed between finger nails they flatten without breaking, or with some crumbling only. The dry capsules of A. serpyllifolia, however, are usually smooth. They are brittle and respond to pressure applied to the top part of the capsule by snapping open lengthwise. Usually they disintegrate entirely. Transverse sections of the mature capsule wall differ in absolute thickness (40-150 µm in A. serpyllifolia; 15-30 µm in A. leptoclados in sections taken through the middle portion of the fruit), as well as in the presence (A. serpyllifolia) or absence ( (A. leptoclados) of a subepidermal layer of large, thick-walled cells (Fig. 2a and b). Next to this, A. leptoclados usually has shorter petals, as well as a different chromosome number (2n = 20 in A. serpyllifolia; 2n = 40 in A. leptoclados). These characters are sufficient to regard A. leptoclados as a separate species next to A. serpyllifolia. It is not possible to further divide A. serpyllifolia by splitting off the taxon macrocarpa. The distinguishing characters between these two given in the literature do not hold; intermediates frequently occur. Other distinguishing characters cannot be found.