Overview

Distribution

National Distribution

Mexico

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

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Global Range: Reported to occur in northern Mexico: Chihuahua, Coahuila, Durango, Nuevo Leon, Zacatecas. In the U.S. it is found only in Texas.

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Tex.; Mexico (Coahuila, Nuevo León, Tamaulipas).
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Physical Description

Morphology

Description

Plants annual. Vegetative stems submersed with elongate inter-nodes, or emersed and short. Flowering stems 6–15 cm, distal internode 4–8.5 cm. Sessile leaves submersed and thin, or emersed and thickened, 5–15 cm × 1–6 mm. Petiolate leaves and stipules not produced. Inflorescences spicate, 7–24-flowered, elongating over several days; spathes 1.2–4 cm; peduncle 4–9 cm, glandular-pubescent when emersed. Flowers 2–10 per inflorescence opening each day; perianth mauve, salverform, tube 2–6 mm, limbs zygomorphic, lobes narrowly elliptic, 8–13 mm, proximal lobe shorter; stamens unequal, lateral stamens 2.7–7 mm, filaments obliquely inflated at center, bent upward apically, glabrous; central stamen 5.9–10 mm, filament linear; style glabrous. Seeds 12–15-winged, 0.7–1 × 0.6–0.9 mm, outer integument composed of additional surface layer of tetragonal to hexagonal isodiametric cells.
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Diagnostic Description

Synonym

Eurystemon mexicanum (S. Watson) E. J. Alexander
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Type Information

Isotype for Heteranthera mexicana S. Watson
Catalog Number: US 937924
Collection: Smithsonian Institution, National Museum of Natural History, Department of Botany
Verification Degree: Original publication and alleged type specimen examined
Preparation: Pressed specimen
Collector(s): E. Palmer
Year Collected: 1880
Locality: Juraz, ca. 100 mi N of Monoclava, on Sabinas River., Coahuila, Mexico, North America
  • Isotype: Watson, S. 1883. Proc. Amer. Acad. Arts. 18: 166.
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Isotype for Heteranthera mexicana S. Watson
Catalog Number: US 33997
Collection: Smithsonian Institution, National Museum of Natural History, Department of Botany
Verification Degree: Original publication and alleged type specimen examined
Preparation: Pressed specimen
Collector(s): E. Palmer
Year Collected: 1880
Locality: Coahuila, Mexico, North America
  • Isotype: Watson, S. 1883. Proc. Amer. Acad. Arts. 18: 166.
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Ecology

Habitat

Comments: Often growing in shallow water and rooted in mud, in ephemeral pools, swales, ditches, pond margins, and resacas (former channels of the Rio Grande that became naturally cut off from the river and often contain stagnant ponds or marshes). There are also disjunct populations on the Texas panhandle which grow on the margins of playa lakes. Grows in an area subject to irregular rainfall; seeds appear to be adapted to survive at least several years in dry soil. 0 - 400 m.

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Ephemeral pools; 0--400m.
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Life History and Behavior

Cyclicity

Flowering/Fruiting

Flowering Jun--Dec.
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Conservation

Conservation Status

National NatureServe Conservation Status

Mexico

Rounded National Status Rank: N2 - Imperiled

United States

Rounded National Status Rank: N1 - Critically Imperiled

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NatureServe Conservation Status

Rounded Global Status Rank: G2 - Imperiled

Reasons: Apparently found on 5 northern Mexico states, where it is suspected to be rare. In the U.S. it occurs in south and northwest Texas, where it is considered rare.

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Notes

Comments

Heteranthera mexicana is very rare and should be considered for national endangered or threatened status. Populations are located in swales and ditches in an area that is subject to irregular rainfall. In several attempts to locate populations during the mid-1980s, the swales were discovered to be dry; yet in 1987, a wet year in south Texas, a population of several thousand individuals was found. This suggests that seeds are adapted to survive at least several years in dry soil.
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