Excerpts from Jim Conrad's
Naturalist Newsletter

Spiny Amaranth, AMARANTHUS SPINOSUS

from the April 18,  2010 Newsletter issued from Hacienda Chichen Resort beside Chichén Itzá Ruins, central Yucatán, MÉXICO
SPINY AMARANTH

Not all of Mérida's street plants were noteworthy ornamentals. Flowering nowadays at the bases of streetlights, along breaking-up sidewalk edges and in low, moist parts of abandoned lots is the plant shown above.

That's the knee-high Spiny Amaranth, AMARANTHUS SPINOSUS, and the very second I saw it a poignant memory flashed through my mind, one from Kentucky farmboy days, of me going out to the pond to fish for catfish, carrying a tin can with a few earthworms in it for bait, barefooted, trying hard to not step on a Spiny Amaranth because its spines HURT!

In the picture you might guess that those pale green, slender items are spikelike flower heads, or inflorescences. Those long inflorescences bear only male flowers. Each male flower consists of five 1/8th- inch long (2 mm) scale-like "tepals" and five stamens. You can some male flowers, with most of the baglike, pollen-producing anthers having fallen off their white, bristly filaments, below:

Spiny Amaranth, AMARANTHUS SPINOSUS, male flowers

Spiny Amaranth's female flowers similarly bear five tepals, but instead of stamens have three spreading stigmas atop an ovary, which eventually matures into an egg-shaped fruit-type known as a utricle. Utricles are bladdery, one-seeded fruits not splitting open at maturity. Female flowers occur in more or less spherical little bunches in the leaf axils -- where the leaves' petioles attach to the stem -- as shown below:

Spiny Amaranth, AMARANTHUS SPINOSUS, female flowers and spine

In that picture you also see where the plant puts its spines -- exactly where they're needed, pointed in exactly the right direction, to deter probing herbivore lips. They're only about half an inch long (15 mm) but sure can make a farmboy jump when they're stepped on just right. In that last picture, toward the top, you can also see fuzzy stigmas atop the ovaries filtering the air for pollen.

Spiny Amaranth is native to tropical America's humid lowlands but now is established as a weed in the tropics worldwide -- it's "pantropical." And as I could already tell you back in Kentucky during the early 1950s, it also occurred well beyond the tropics. On our farm it was limited to the barnyard, where the richest, most trampled-on soil was.