Eryngium prostratum Nutt. ex DC.

Spreading Eryngo

© DETenaglia

Family - Apiaceae

Habit - Perennial forb with thin, fibrous roots. Herbage glabrous, not glaucous.

	Plant with U.S. penny for scale.
© SRTurner

Stems - Prostrate, creeping, to 50 cm, rooting at the nodes.

From slightly thickened roots and a small cormlike base, creeping, repent, herbaceous, to +40cm long, branching, glabrous, ribbed or angled, with a slight carrot fragrance.

	Stem and node.
© SRTurner

Leaves - Opposite or more commonly whorled and basal, glabrous. Blades entire or with a pair of narrow basal lobes, the venation netted. Basal leaves long-petiolate, the blades 1-4 cm long, lanceolate to broadly ovate, narrowed or rounded at the base, rounded to bluntly pointed at the tip, the margins entire or with few, relatively coarse, blunt teeth. Leaves at the nodes of the stems similar to the basal leaves, but sessile or mostly short-petiolate, the blades 0.4-2.5 cm long.

	Basal leaves.
© SRTurner

	Basal leaf, adaxial.
© SRTurner

	Basal leaf blade, abaxial.
© SRTurner

	Stem and leaves.
© SRTurner

	Lobed leaf.
© SRTurner

	Pressed leaves.
© DETenaglia

Inflorescences - Cylindrical heads 0.4-0.9 cm long, axillary, solitary, mostly long-stalked, grayish blue. Peduncle to 3cm long, glabrous, ribbed. Bracts subtending each head 5-10, 2-12 mm long, linear to narrowly lanceolate or narrowly oblanceolate, sharply pointed at the tip, the margins entire or with a few minute teeth. Flowers numerous, sessile, each subtended by a narrowly lanceolate bractlet 0.5-0.8 mm long.

	Inflorescence.
© SRTurner

	Inflorescence structure.
© SRTurner

	Single inflorescence.
© SRTurner

Flowers - Sepals 5, 0.5-0.8 mm long, ovate to broadly ovate, entire, usually with broad, thin, pale margins. Calyx tube .7mm long in flower, 1mm broad, covered with white glands. Petals 5, obovate, rounded or shallowly notched at the tip, blue or less commonly white. Stamens 5, alternating with the petals, erect, exserted well beyond the corolla. Filaments glabrous, lilac, 1.3 mm long. Anthers brownish-purple, 0.2 mm long. Styles 2, spreading, 1mm long, glabrous, purplish-blue at the apex, fading to white at the base, expanded on one side into a green stylopodium, persistent in fruit and elongating slightly. Stylopodia erect and somewhat wrapped around the style, to 0.3 mm long. Ovary inferior, 2-locular, with minute, white tubercles.

	Flowers.
© SRTurner

	Flowers.
© SRTurner

Fruits - Schizocarps 0.5-0.8 mm long, broadly oblong-obovate in outline, with minute, white tubercles.

Flowering - May - November.

Habitat - Swamps, bottomland forests, pond margins, streambanks, fens, swales, pastures.

Origin - Native to the U.S.

Lookalikes - None.

Other info. - This interesting little species can be found in the southeast corner of Missouri, and also occurs across much of the southeastern continental U.S. Due to its small size it is often overlooked, but once spotted it is easily identified by its unique blue flowering heads. It does not much resemble its closest common sibling in Missouri, which is Eryngium yuccifolium, a tall, upright plant with globose greenish inflorescences. These plants also show no obvious similarity to those more typical of the Apiaceae (carrot or hemlock family). The relationship is hidden in the floral details.

Photographs taken at the Crowley Ridge Conservation Area, MO., 6-14-03 (DETenaglia); also at McGee Creek State Park, Atoka County, OK, 7-26-2016, about 4.5 miles southeast of Benton, Scott County, MO, 10-5-2017, and at Big Cane Conservation Area, Butler County, MO, 6-9-2023 (SRTurner).