Pignut (Hoffmannseggia glauca)

Synonyms: Hoffmannseggia densiflora, Hoffmannseggia falcaria, Hoffmannseggia stricta, Hoffmannseggia demissa, Hoffmannseggia alpina, Hoffmannseggia chinensis, Caesalpinia falcaria, Caesalpinia glauca, Caesalpinia chicamana, Larrea glauca, Larrea densiflora, Poinciana hirsuta

Common Names: Hog potato, hogpotato, Indian rushpea, Indian rush-pea, waxy rush-pea, camote de raton, shoestring weed

Description:

Pignut (Hoffmannseggia glauca) is a low perennial in the pea family, native to the dry Southwest and southern Great Plains of the United States, south into Mexico and again in South America [3][4][5]. It grows from deeply buried creeping roots that carry small, nut-like tubers about 10 to 15 inches down ? the source of both its names and its reputation, since those tubers are very hard to dig out [2]. It is a native plant rather than a foreign one, but it behaves as a weed of roadsides, fields, and croplands, and MISIN tracks it so that any occurrence outside its home range is spotted early [2][3].

Habit:

Pignut is a small plant ? the stems stand only about 8 to 12 inches tall, and rarely reach much past a foot [1][2][3]. The leaves cluster near the base of the plant rather than up the stem, and each one is twice-divided: a main leaf stalk carries several side branches, and each of those carries many tiny oblong leaflets, giving the whole leaf a soft, ferny look [1][2].

The detail that settles it is the glands. The stems, leaf stalks, flowers, and pods are all dotted with tiny, distinctive tack-shaped glands ? they look like miniature pins pushed into the surface, and on the flower stalks they are reddish [1][2]. Few plants carry anything like them.

Look from late spring through early fall ? roughly May into September, when it flowers, with pods following from June into October [2]. The flowers make it easy: a spike of pea-shaped blooms held up above the low mound of leaves, each about half an inch long, bright yellow and aging to orange-red, so a single spike often shows both colors at once [1][2][3]. Afterward come flat pods about an inch to an inch and a half long, straight or slightly hooked, which drop readily [1][2]. Look on bare, disturbed, sandy or alkaline ground ? roadsides, fence lines, ditches, and field edges [1][3].

At-a-glance cues:

1. Tiny tack-shaped glands dotting the stems, leaf stalks, flowers, and pods ? reddish on the flower stalks [1][2]
2. A low plant, 8 to 12 inches tall, with twice-divided ferny leaves bunched near the base [1][2]
3. Spikes of half-inch pea flowers held above the leaves, bright yellow fading to orange-red [1][2][3]
4. Flat pods about 1 to 1.5 inches long that fall off readily; nut-like tubers deep on the roots [1][2]

Leaves:

1. Arrangement: alternate, with most leaves clustered near the base of the plant [1]
2. Type: bipinnately compound ? twice-divided, with 5 to 11 side branches, each carrying 4 to 12 pairs of small leaflets [1]
3. Size: whole leaf about 2 to 5 inches (5 to 13 cm) long [1][2]
4. Leaflets: oblong, about 3 to 8 mm long ? roughly an eighth to a quarter inch [1][2]
5. Surface: smooth to minutely hairy, dotted with tiny tack-shaped glands on the leaf stalks [1][2]

Stems:

1. Habit: herbaceous perennial, about 6 to 12 inches (15 to 30 cm) tall; usually several stems per plant, renewed each year [1][2]
2. Surface: dotted with tiny, distinctive tack-shaped glands [2]
3. Roots: deeply buried creeping underground stems (rhizomes) bearing nut-like tubers about 10 to 15 inches below the surface [1][2]

Flowers:

1. Color: bright yellow, aging to orange-red ? a spike often shows both at once [1][2][3]
2. Shape: pea-shaped, with 5 spreading petals, not radially symmetrical; about 1 cm (roughly half an inch) long [1][2]
3. Arrangement: an elongated cluster (raceme) at the stem tip, held above the leaves [1]
4. Glands: flower stalks carry distinctive red stalked glands [1]
5. Sex: perfect ? each flower has both male and female parts [1]
6. Bloom time: about May to September; sources give ranges from March or April through September [1][2][3]

Fruit and seeds:

1. Fruit type: a flattened, oblong pea pod, straight to slightly hooked at the end [1][2]
2. Size: about 1 to 1.5 inches (2 to 4 cm) long and 5 to 8 mm wide [1][2]
3. Ripening: pods form from June into October [2]
4. Dispersal: pods are readily deciduous ? they drop off the plant easily [1]
5. Seeds: several per pod, typically about 1 to 6 [1][2]
6. Tubers: small, nut-like tubers form on the deep roots and are the plant's main means of persisting and spreading [2]

Habitat:

Pignut is native to the United States ? the USDA PLANTS Database records it as native across the lower 48 [5]. Its home range runs through the dry Southwest and southern Great Plains: southern California, Arizona, Nevada, New Mexico, southern Colorado, southern Kansas, southern Oklahoma, and Texas, continuing south into Mexico, and appearing again in South America from Bolivia southward [1][3][4]. It is not a Great Lakes plant, and no record of it from the MISIN region turned up in the sources reviewed.

Within that range it grows on sandy and alkaline soils, generally below about 5,000 feet (1,524 m) [1]. It is a plant of open, bare, disturbed ground rather than intact habitat ? it is common along roads and turns up as an agricultural weed, and it forms large colonies on roadsides, fence lines, ditches, and fields [1][2][3].

Reproduction:

Pignut spreads two ways, and the underground half is what matters most.

Below ground, it creeps ? and it goes deep. The plant grows from deeply buried creeping roots that carry small, nut-like tubers roughly 10 to 15 inches below the surface [1][2]. New stems come up from that network each year [1]. This is the whole difficulty with the plant: the tubers sit well below the reach of ordinary digging or tillage, and they are described plainly as difficult to remove from the soil [2]. Pull the top and the tubers simply send up more.

It also sets seed. Flowers open from about May into September, and flat pods form from June into October, each holding roughly one to six seeds [1][2]. The pods fall off the plant readily once ripe [1].

There is a third route worth knowing, because it is the one people control: the plant moves on equipment. Roots and root fragments carried on machinery spread it from an infested field into a clean one, which is why cleaning equipment before moving between sites is a standard recommendation [2].

For timing, the practical points are simple. Remove plants before pods ripen to stop new seed, and understand that getting rid of an established patch means getting the tubers ? grubbing has to be repeated annually for at least two years to work [2].

Impact and Damage:

Pignut is not reported to be a health hazard. Its tubers are in fact edible: they were valued as food by Native peoples and are eaten by wildlife, which is where the names pignut, hog potato, and the Spanish camote de raton ? "mouse's sweet potato" ? come from [3]. No source reviewed here reports toxicity to people, pets, or livestock.

The documented problem is agricultural. Pignut is a common weed of croplands and roadsides within its range, and it forms large colonies on disturbed ground [1][2][3]. Because it grows from tubers 10 to 15 inches down, it is hard to remove, and as a perennial it is "difficult to control mechanically" ? partial removal of the root system does not work [2]. That is the practical cost: a persistent, deep-rooted weed in fields and along field edges.

What is not documented deserves equal weight here. This is a native plant, not an introduced one [5]. The USDA PLANTS Database records no noxious status, no invasive status, and no legal status for it at the federal level [5]. No study quantifying crop-yield loss or economic damage surfaced in the sources reviewed, and no peer-reviewed research on its ecological effects was located. Nothing found describes it displacing native vegetation in natural areas. Read this sheet as a description of a native weed of dry-country farmland ? not as evidence of an invader in the Great Lakes.

Similar species:

No commonly confused species in the MISIN region.

Monitoring and rapid response:

Signs to watch for:

1. A low, ferny-leaved plant under a foot tall on bare, disturbed, sandy ground ? roadsides, fence lines, ditches, and field edges [1][2][3]
2. From May into September, spikes of half-inch pea flowers held above the leaves, bright yellow aging to orange-red [1][2][3]
3. Tiny tack-shaped glands on the stems, leaf stalks, flowers, and pods ? reddish on the flower stalks [1][2]
4. Flat, inch-long pods from June into October, dropping off readily [1][2]
5. Large colonies spreading across open, disturbed ground [3]

What you can do:

1. Grub out small patches ? and get every tuber. Small infestations should be dug out, taking care to remove all of the nut-like tuberous roots [2]. Expect to repeat the grubbing annually for at least two years for good control [2].
2. Be realistic about the depth. The tubers sit 10 to 15 inches down and are hard to lift out of the soil, so a shallow pull accomplishes little [2]. Unless the entire root comes out, control is not likely to succeed ? as a perennial, this plant is difficult to control mechanically [2].
3. Cut or pull plants before the pods ripen so no new seed is set, and bag what you remove [1][2].
4. Clean your tools and equipment. Roots and root fragments hitchhike on machinery and start new patches ? clean them off before moving to uninfested ground [2].
5. Catch it early. Surveying fence lines, roadways, ditches, and other likely spots and promptly removing new plants keeps it from establishing in the first place [2].
6. Natural area crews and landowners: on cultivated ground, repeated shallow cultivation every three weeks or so, not letting new shoots grow more than about ten days after they emerge, is used to wear the plant down [2]. Note that no biological control agents are approved for this species [2].

When to call a professional:

1. Established colonies where hand-grubbing cannot reach or keep up with the tuber network.
2. Cropland or right-of-way situations needing a coordinated, multi-year plan.
3. For chemical control options, contact a licensed applicator or your local cooperative extension office.

Report sightings to MISIN. Help track this species' spread by submitting observations through the MISIN web site or the MISIN mobile app (Android, iOS, Windows, and macOS). Photos at multiple angles paired with a precise GPS location are the most valuable data for confirming new occurrences and triggering rapid-response review.

Credits:

1. SEINet, Arizona?New Mexico Chapter. Hoffmannseggia glauca (Ortega) Eifert ? Indian rushpea. Southwest Environmental Information Network. swbiodiversity.org
2. County Weed Directors' Association of Kansas. Pignut (Hoffmannseggia glauca) ? description and control practices; sourced to Kansas Department of Agriculture K.A.R. 4-8-36, revised May 20, 2020. sedgwickcounty.org
3. Lady Bird Johnson Wildflower Center, University of Texas at Austin. Hoffmannseggia glauca (Indian rushpea). Native Plant Database. wildflower.org
4. POWO (2026). Hoffmannseggia glauca (Ortega) Eifert. Plants of the World Online, Royal Botanic Gardens, Kew. powo.science.kew.org
5. USDA NRCS PLANTS Database. Hoffmannseggia glauca (Ortega) Eifert (Indian rushpea), symbol HOGL2. plants.usda.gov

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