1927, Iris Rivularis
Addisonia volume 12, page 11, plate 390, 1927
Native of Florida and Georgia
Family Iridaceae, Iris Family
The watersheds of different rivers commonly harbor flags of a single species or endemic plants. The dominating iris of the watershed of the upper Saint John's River is Iris Carolina which, however, is not an endemic. Beyond the northern crest of this water-shed, as the land gradually falls off toward the Saint Mary's River and southern Georgia, an iris of a different relationship appears. It occurs in colonies, often very extensive, along streams tributary to the Saint Mary's River. The most thriving colonies grow on the middle ground along the streams in a mixture of sand and clay deposited by the flood waters.
This kind of a habitat has developed a very vigorous plant one that is very tenacious of life. The roots and rootstocks which store the vitality and form the anchors continue to grow whether washed nearly clean of soil or buried deep in it. The apical growth, with sufficient energy stored in the rootstock to withstand exposure to the air or smothering in the soil, at once adjusts itself to seeking its proper depth in the newly-made level of the habitat.
The home of the early ancestors of this iris evidently was in the highlands. Whatever its ancestors may have been, the plant under consideration reached its present geographic range and status through changes in its structure adapted to changes in elevation, topography, and climate. Before the land was much sculptured, this plant, or its more immediate ancestors, may have occupied vast flat areas, as the prairie blue-flag (Iris savannarum) now does in peninsular Florida. Later on when the land rose and streams were formed, gradually cutting more deeply into the surface, our subject retreated to the vicinity of streams, selecting places where the water-table was suited to its demands for moisture.
It grows either on the otherwise barren sandbars with no protection, or closely associated with the thickets of willows, alders, and other many-stemmed shrubs of river shores. When in flower the colonies, with their violet or purple perianths, are equally showy, whether with the bare sand as a background or the greenery of a thicket. The pods stand erect until maturity when their weight bears down the flower-stem until the fruits lie on the ground, where they gradually decay and allow the seeds to be floated away with the next freshet. The type specimens were collected by the writer along a stream south of the Saint Mary's River on the road from Yulee, Florida, to Kingsland, Georgia. Plants of the original collection survived several winters in the cold frames at the Garden, and the winter of 1925-26 in the beds in the iris plantation.
The sylvan-flag has a rather stout fleshy horizontal rootstock. The leaves are erect, usually two or three together. The blades are linear-attenuate, usually one half to three quarters of an inch wide, bright green. The flower-stalk is one to two feet tall, rather stout, green, often bearing one or two leaves. The flowers are solitary or two together terminating the flower-stalk, and frequently in the axil of the upper leaf. The involucre subtending the flowers has two main bracts, the longer one exceeding the flower, attenuate. The pedicel is one and a half to two inches long, about as long as the hypanthium. The hypanthium surrounding the ovary is three-angled, green. The perianth-tube is narrowly campanulate, bluntly three-angled, at least two thirds as long as the ovary. The three sepals are arching, remate, two and a quarter to two and three quarters inches long. The blade is broadly oval, deep-violet above, with white radii diverging from the green or yellow-green crest which vanishes much below the middle of the blade. The claw is nearly or quite three eighths of an inch wide, light green but striped with deeper green, all shading into the yellow-green at the base of the blade. The three petals are narrowly spatulate, about two inches long; the claw is whitish and finely striate with green veins; the blade is violet but slightly paler than the violet of the sepal-blade. The three stamens are nearly an inch and a quarter long. The filaments are violet-tinged above the base. The anthers are much longer than the filaments. The three style-branches are broadly linear, a little less or little more than an inch and a half long, fully a quarter of an inch wide, green without, lavender-tinged within. The stigma is two-lobed. The style-appendages are lanceolate, nearly or quite a half inch long, pale-violet or lavender, sparingly and coarsely erose. The capsule is oval, varying to somewhat ovoid or obovoid, an inch and a half to two and a half inches long, bright green, slightly beaked, bluntly three-angled, about as long as the pedicel. The seeds, borne in one row in each capsule-cavity, are corky, nearly or quite a half inch in diameter.
John K. Small.
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