Cacti are some of the hardiest plants. They last decades on minimal water. These little markers have a central cut out giving them that hollow look.
The small version of the markers measure approximately 1/2" (12 mm) long by 5/16" (8 mm) wide, and weigh less than a gram. They are shown on a 6 mm ring and a 12 mm lobster clasp. The 6 mm ring comfortably fits knitting needles size US4 and smaller. The 8 mm ring comfortably fits knitting needles size US6 and smaller.
The large version of the markers measure approximately 13/16" (20 mm) x 1/2" (12 mm), and weighs about a gram. These are available on all ring and hook sizes, and are shown on a 10 mm ring and 12 mm lobster clasp.