Fynbos

Fynbos (Afrikaans, "fine bush") is the low, hard-leaved, fire- and drought-adapted shrubland that covers a belt of South Africa's southwestern and southern Cape. Fynbos is the dominant vegetation of the Cape Floristic Region, one of only six floral kingdoms recognised on earth and, by area, the smallest of them. That region covers less than half a percent of Africa's land and holds about a fifth of the continent's plant species.

What the shrubland is made of

• The proteoid layer. Broad-leaved shrubs of the protea family (Proteaceae), the tallest plants in the system and its visible overstorey.
• The ericoid, or heath, layer. Small, narrow, often rolled leaves. This layer holds the majority of fynbos species, and it is a crowded neighbourhood: heaths (Ericaceae) sit alongside daisies (Asteraceae), blacktips (Bruniaceae), and legumes (Fabaceae), rooibos's own family⁵. Rooibos belongs here, a quiet understorey shrub rather than a headline act.
• The restioid layer. Wiry, grass-like reeds (Restionaceae) that do a grass's job on nutrient-poor soils. This family is one of the plant groups botanists use to define fynbos itself.

Between them, SANBI records, the fifteen largest families in the biome account for about 70 percent of its species, and seven families occur here and are all but absent everywhere else. Rooibos, one species in a large Cape legume genus (Aspalathus, close to 280 species), is one working part of the second layer.

The soil

Fynbos grows on well-leached soil weathered mostly from Cape Supergroup sandstone, ground SANBI itself describes simply as infertile.

Rooibos answers the same poor ground with a legume's oldest trick. Nodules on its roots house nitrogen-fixing bacteria that draw nitrogen from the air the plant cannot get from the soil.

The Fynbos Biome, in SANBI's own classification, is really two related shrublands: fynbos proper, on sandstone, and renosterveld, a shrubland dominated by renosterbos (a daisy relative) on richer clay and shale soils derived from a different geology. Rooibos grows on acid, sandy soils.

Fire, the shrubland's clock

SANBI records that fynbos must burn at somewhere between six and forty-five years of age to sustain its full plant list. A shrubland left unburned for too long becomes senescent, and forest and thicket species begin invading. Burn it too often, on the other hand, especially outside the late-summer season the system evolved with, and the slower-maturing shrubs never reach seed-bearing age before the next fire kills them.

Two plant strategies answer that clock, and wild rooibos itself sorts cleanly into both of them: reseeders killed by the burn and rebuilt from a heat-triggered seed bank, resprouters that survive it outright and regrow from a fire-hardened base.

A crowded family tree

The genus Aspalathus holds close to 280 species, almost every one of them a Cape endemic, and only a handful were ever brewed as tea at all. A short mountain range or two over, a different legume tribe of the same shrubland produced honeybush (Cyclopia), the fynbos's other caffeine-free infusion and, despite the family resemblance on a shelf label, not a close relative of rooibos in the genetic record.

The insects

The honeybee that turns up at a rooibos flower every spring takes the nectar and leaves without moving a grain of pollen; the actual work is done by a short list of solitary bees and wasps built to spring the flower's particular lock.

A protected shrubland, and what threatens it

Wild rooibos

Wild rooibos is hand-cut from the veld on a rule the small-scale Suid Bokkeveld harvesters worked out: a moderate cut, an inch above the previous scar, and a harvest once every two years.