The geographical distribution

The geographical distribution area is identical to the drier zones of Mexico with a maximum

precipitation of up to 1000 mm/year. These precipitations, however, are very unequally distributed over the year and mainly occur in the four summer months as heavy thunder showers. The rest of the year is dry. The majority of Coryphantha spp. grow in regions with less than 600 mm/year precipitation, i.e. dry and very dry zones, but the marginal areas of distribution are located in moderately humid regions. Summer in the whole distribution area is very hot, but in the wintertime short cold periods and nightly frosts are not unusual, mainly in the north.

The world’s simplest land plants

The world’s simplest land plants do not have

flowers or seeds. Instead, they reproduce by

releasing tiny cells called spores. Spores are

far smaller and simpler than seeds, and they

spread by water or on the wind. Seedless plants

include liverworts, mosses, and horsetails,

as well as all the world's ferns (see pages

30–31). Unlike seed plants, a seedless plant’s

life cycle alternates between two distinct plant

forms: one that produces spores, and one that

produces sex cells (sperm and eggs). Sometimes

the two plant forms look similar, but often they

are completely different, both in size and shape.