25.2: Geography of Vegetabilia
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- Valeria Hochman Adler
- Reedley College
While taiga forest looks similar in Alaska (North America) and Patagonia (South America), a closer look will immediately reflect that species, genera and even families of plants are quite different. As an example, both Alaska and Patagonia forests include large conifers, but while in Alaska we frequently see members of Pinaceae family like spruces ( Picea ) or firs ( Abies ), in Patagonia these trees are absent and “replaced” with superficially similar trees of Araucariaceae and Podocarpaceae conifers.
Analogously, Arizona desert is similar to African Kalahari but while American deserts are rich with cacti, similarly looking African plants belong to completely different group, succulent spurges ( Euphorbia ). The effect of these differences on the botanically educated traveler is a bit similar to the nightmare when you first see a familiar thing but approach it—and realize that this is something completely alien and strange.
These floristic differences are due to the various geological and biological histories of these places. Plant biogeography studies them, explains them and creates the floristic kingdoms classification (Figure \(\PageIndex{1}\)) which takes into account not ecological but taxonomical (phylogenetic) similarities and differences.
There are only five floristic kingdoms:
Holarctic Most of North America and temperate Eurasia. Holarctic kingdom is largest, it covers two continents and most of Northern hemisphere. Typical representatives are pines ( Pinus ) and oaks ( Quercus ).
South American From South Florida to Patagonia and Antarctic islands. Aroids (Araceae family) and bromeliads (Bromeliaceae) are very common South American groups.
African Excluding Mediterranean Africa (very north of the continent). African acacias ( Senegalia ) are common to the most of savannas there.
Sometimes, botanists separate the southern tip of Africa into smallest Cape floristic kingdom which has multiple endemic plant genera (like Berzelia , kolkol) and even whole families.
Indo-Pacific From India to pacific islands including Hawaii. This kingdom is especially rich of orchids (Orchidaceae); tropical pitcher plants ( Nepenthes ) grow only there.
Australian Australia, Tasmania and New Zealand. Numerous specific plant groups, including Eucalyptus , Banksia and many others.
Every plant group has a specific range —the area of distribution. There are multiple common ranges, e.g., circumpolar (groups distributed across North Pole, both in North America and Eurasia, like spruces, Picea ) or Gondwanian (groups distributed in the South Africa, Australia and South America, like protea family, Proteaceae). Sometimes, there are disjunctions (breaks in range); a typical explanation for the disjunction is long-distance dispersal (like for ispaghula, Plantago ovata in California and West Asia) or extinction in the connecting places (like for tulip tree, Liriodendron in China and Atlantic states).
Recently, many plants became invasive after being introduced willingly (e.g., as forage plants) or accidentally (e.g., with seeds of other plants). These plants (like Eurasian spotted knapweed, Centaurea stoebe in North America, or North American box elder, Acer negundo in Eurasia) are often noxious since they tend to destroy the native vegetation.
It is frequently said that humans stated the new epoch of Earth life, homocene —era of Homo sapiens dominance, homogenization and great extinction of the flora and fauna. We need to stop that!