29. Equisetaceae

The horsetail family. A single genus family (Equisetum) with about 20 species. Like cycads, Equisitum are considered "living fossils" - in their case the lineage goes back to the Paleozoic Era. Among their common names are horsetail, due to their appearance, puzzlegrass, and scouring-rush, this due to the fact that the tough stems make good scouring brushes.

28. Droseraceae

The sundew family. Three genera and approx. 180 species, all carnivorous, the most famous being the venus fly trap (Dionaea muscipula). Less well known is the waterwheel plant (Aldrovanda vesiculosa), a sort of aquatic variation of the same idea.

27. Dioscoreaceae

The yam family. Nine genera and approx. 715 species. The familiar edible yam belongs to the Dioscorea genus, which is named after the ancient Greek botanist Pedanius Dioscorides. Some of these yams contain steroidal hormones that can be used for contraception.

26. Dennstaedtiaceae

One of the fern families. 10 genera and 240 species. One of the most common ferns, Pteridium aquilinum (brackenfern), is in this family. The term bracken is synonymous with the genus Pteridium.

25. Cyrillaceae

A tiny family containing only two genera and two species. The one I have encountered is Cyrilla racemiflora, also known as swamp titi. It is native to tropical America and also found in the southeastern U.S.

24. Cycadaceae

The cycad family. Only one genus, Cycas, with approx. 113 species. Cycads have an ancient lineage; they are leftover from the Jurassic period, and native only to the Old World tropics. They generally live a long time, sometimes over 1,000 years. The best collections of cycads I have ever seen, which is one of the best in the world, is at Lotusland in Santa Barbara, CA (above).

23. Crassulaceae

The stonecrop or orpine family. Approx. 35 genera and 1400 species (the number of genera is in dispute). Most people would recognize these plants as succulents. Jade (Crassula ovata), Kalanchoe, Sedum, Dudleya, Sempervivum, Echeveria.