Blackwater Flower · Rheomarginis confluentis

A perennial submerged plant that spends most of the year underwater. It raises a flower stalk neither where flooding is deepest nor longest, but only at the chemical border where two water masses mix and the acidity shifts sharply, just once. Because its appearance cannot be explained by water level, records long stayed unstable. Submerged, it spreads slender dark-olive leaves; when the waters meet it sends a reddish stalk to the surface and opens a single pale green-white waxy flower. It can stay in the air only the few days the mixing lasts.

Specimen Plates

8 plates · click to enlarge

PLATE I

PLATE II

PLATE III

PLATE IV

PLATE V

PLATE VI

PLATE VII

PLATE VIII

Field Note

Habitat

Igapó (seasonally flooded blackwater forest) of the lower Rio Negro, northern Brazil. In the rainy season the forest floor is fully submerged for months. It appears only at the rim of confluences, where clear tributary water enters the acidic black water and the water's nature briefly changes.

Local name

"Flower of the Border" / "Flower where the water turns two colours" — named for standing at the line between black water and clear.

Folklore

Fishermen of the Rio Negro treat the place where it stands as a sign that the waters are about to change, using it to read that year's fish routes. The bank where it stands is said to grow calm for a while. It is passed down not as the supernatural, but as local knowledge built from long observation.

Locator

Coordinates

2.5°S 60.7°W

Igapó (seasonally flooded blackwater forest) of the lower Rio Negro, northern Brazil

Record

Almost no specimens, and no firm records, remain.

For it appears not by water level, but only where the water's nature changes just once.

Northern Brazil, the Rio Negro — a tale of a forest drowned in black water.

It spends most of the year on the riverbed, showing itself for only a few days.

Where clear tributary water enters the acidic black water — only at that border does a slender flower stalk rise.

It blooms neither where the water is deepest, nor where it stays longest.

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Classification

Classification & specimen data

Scientific name

Rheomarginis confluentis T. Okabe, 1968

Taxonomy

Plantae › Angiosperms › Dicotyledons › Rheomarginales › Rheomarginaceae › Rheomarginis › confluentis

Voucher

AVF-016 · Holotype
Archive of Vanished Flora (AVF)

Conservation

✝ EX — Extinct Last seen 1971

Collector

E. Mori
1968-05-05

Synonym

Rheomarginopsis confluentis N. Drei, 1966

Protologue (Latin)

Herba parva rosulata, foliis crassis glaberrimis, floribus parvis stellatis. Typus: Igapó (seasonally flooded blackwater forest) of the lower Rio Negro, northern Brazil. Species iam extincta.

Discovered / Described

1968 / 1968

Height

5〜15 cm

Life form

Perennial herb

Phyllotaxy

Alternate

Chromosome

2n = 22

Flowering

A brief flowering (a few days)