Naming Cactus and Succulents ... 4/5

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Knowing that the genera name (Stenocereus) is like a surname, you could say that another Stenocereus species may look similar (large and cereoid), in much the same way Lucy Jones Mother or Daughter may look like her. Although another stenocereus may look different (Stenocereus eruca is prostate and creeps along the ground) somewhere there will be a similarity e.g. the flower or fruit structure.

In the plant kingdom flower and fruit structures were usually much less changeable among similar plants than leaf, stem, or root structures which can change due to environmental conditions (eg light, water, growing conditions), so it is best to concentrate on reproductive structures as a means of classifying plants into similar groups. As an aside plants of similarity are more likely to pollinate with each other to form hybrids than completely different genera/families.

An example of how the SAME plant can look DIFFERENT is the Melocactus genus, when first discovered many Melocactus species were described and named, but on closer investigation it turns out that the species within the genera are highly variable (usually means it is a "young" genera in evolutionary terms and hasn't "settled" down to it's final form) and there are a lot fewer species (and more varieties or even forms) than first described. Differences can also be brought on by growing, soil or weather conditions in the locality.

A complete breakdown of the plant kingdom in summary

Seed-bearing plants are divided into two large groups, the gymnosperms (naked seeds) e.g. conifers, cycads; and the angiosperms (vascular seeds.), which have typical flowers and seeds clothed with some kind of fruit. Angiosperms are further divided into monocotyledons, having one leaf (cotyledon) emerging from the seed like grasses, palms, and aloes; and dicotyledons, having two cotyledons, like beans, roses, and cacti (although in highly evolved cacti the cotyledons are hardly visible in seedlings - just 2 little bumps. In Opuntias they are quite pronounced).
Cacti are further distinguished by petals attaching above the ovaries (inferior ovary) , and the presence of the areole, a special structure which may form spines (modified leaves), flowers/fruit, or another shoot - found in no other plant family.

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