Amaranthus spinosus L.
  Dicotyledoneae   Amaranthaceae   Amaranthus

Amaranthus spinosus
© Copyright Jean Obrist 2012 · 1
Amaranthus spinosus

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FamilyScientific name @ source (records)
Albuginaceae  Albugo amaranthi @ BPI (1)

Albugo bliti @ BPI (16)
Chionosphaeraceae  Stilbum spraguei @ BPI (1)
Coccinellidae  Coccinella septempunctata @ I_LB (1)
Lygaeidae  Nysius terrestris @ BPBM_TCN (1)
Miridae  Lygus lineolaris @ MEMU_ENT (11)

Reuteroscopus diffusus @ AMNH_PBI (7)

Reuteroscopus ornatus @ AMNH_PBI (4)

Spanagonicus albofasciatus @ MEMU_ENT (9)

Taylorilygus apicalis @ MEMU_ENT (1)
Mycosphaerellaceae  Cercospora brachiata @ BPI (1)
Turritellidae  Vermicularia dematium @ BPI (1)

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Delaware Wildflowers  •  Scientific names

Amaranthus spinosus L. Spiny Amaranth
Amaranthaceae — Amaranth family
Amaranthus spinosus
Carousel Farm Park
July 1999

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Photos copyright David G. Smith

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Amaranthus spinosus  L.

Spiny Pigweed

Amaranthus spinosus plant

Family - Amaranthaceae

Habit - Annual monoecious forb.

Stems - Ascending to erect, to 1.5 m, mostly glabrous, with conspicuous pairs of spines at most nodes.

Amaranthus spinosus stem Stem.

Leaves - Mostly long-petiolate, with blades 2-10 cm long, narrowly ovate to ovate, bluntly or sharply pointed, narrowed or tapered at the base, glabrous or nearly so.

Amaranthus spinosus leaves Leaves.

Inflorescences - Dull or grayish green, occasionally reddish-tinged; axillary and terminal; the axillary inflorescences dense, small, globose clusters or elongate spikes; the terminal inflorescence a spike or panicle with few ascending branches; the flowers often grouped into discontinuous clusters or regions along the basal portions of the spikes; the tip straight or somewhat curved at maturity; the main axis and branches glabrous or nearly so. Bracts 0.5-1.0 mm long, shorter than the sepals, lanceolate to linear, narrowed or tapered to a sharply pointed tip, with a thickened green midrib and relatively narrow, thin, papery margins, the midrib not or only slightly extending beyond the main body as a minute, sharp point.

Amaranthus spinosus node Globular cluster of flowers in the stem axils.

Amaranthus spinosus spine Spines subtending the globular clusters.

Flowers - Staminate flowers with 5 sepals, these 1.0-1.6 mm long, somewhat outward-curved, oblong-lanceolate, sharply pointed. Pistillate flowers with 5 sepals, these 1.0-1.6 mm long, otherwise similar to sepals of staminate flowers. Stamens 5. Stigmas 3, ascending to erect. Ovule 1.

Amaranthus spinosus flowers Flowers.

Fruits - Fruits 1.5-2.0 mm long, dehiscing irregularly, the surface somewhat roughened or wrinkled above the midpoint when dry. Seeds 0.7-1.0 mm in diameter, rounded along the rim, the surface black, shiny.

Flowering - June - October.

Habitat - Waste ground, cultivated fields, disturbed sites, roadsides, railroads.

Origin - Native to tropical America.

Other info. - This introduced weed can be found throughout Missouri and can be quite common in the habitats mentioned above. In general, plants in the genus Amaranthus are difficult to identify to species, but this one is an exception to the rule. The stout spines at the nodes are diagnostic.

A. spinosus is edible and is best picked as a young plant. Older plants become fairly stout and have a woody texture.

Photographs taken off Main St., Ellington, MO., 7-18-04.

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Following modified from Taiwan Biodiversity National Information Network
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Kingdom Plantae  
 Phylum Tracheophyta  
 Class Magnoliopsida  
 Order Caryophyllales  
 Family Amaranthaceae  
 Genus Amaranthus  
  Amaranthus spinosus    L. 
Provider: Ching-I Peng 
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Citation: Flora of Taiwan 2nd ed. 2: 398, 1996; Wu, S. H., C. F. Hsieh, and Marcel Rejmanek. 2004. Catalogue of the Naturalized Flora of Taiwan. Taiwania
Name Code: 202675
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Amaranthus spinosus L.
spiny amaranth

Image of Amaranthus spinosus

General Information
Symbol: AMSP
Group: Dicot
Family: Amaranthaceae
Duration: Annual
Growth Habit : Forb/herb
Native Status : CAN   I
HI   I
L48   N
PB   I
PR   N
VI   N
Other Common Names: spiny pigweed
Data Source and Documentation
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green round image for nativity Native blue round image for introduced Introduced ocre round image for introduced and nativity Both white round image for no status Absent/Unreported
image for native, but no county data Native, No County Data image for introduced, but no county data Introduced, No County Data both introduced and native, but no county data Both, No County Data
Native Status:
lower 48 status L48    Alaska status AK    Hawaii status HI    Puerto Rico status PR    Virgin Islands status VI    Navassa Island NAV    Canada status CAN    Greenland status GL    Saint Pierre and Michelon status SPM    North America NA   


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Steve Hurst. Provided by ARS Systematic Botany and Mycology Laboratory . United States, AZ. Usage Requirements .

Britton, N.L., and A. Brown. 1913. An illustrated flora of the northern United States, Canada and the British Possessions. 3 vols. Charles Scribner's Sons, New York. Vol. 2: 3. Provided by Kentucky Native Plant Society . Scanned by Omnitek Inc . Usage Requirements .




Click on a scientific name below to expand it in the PLANTS Classification Report.
Rank Scientific Name and Common Name
Kingdom Plantae – Plants
Subkingdom Tracheobionta – Vascular plants
Superdivision Spermatophyta – Seed plants
Division Magnoliophyta – Flowering plants
Class Magnoliopsida – Dicotyledons
Subclass Caryophyllidae
Order Caryophyllales
Family Amaranthaceae – Amaranth family
Genus Amaranthus L. – pigweed
Species Amaranthus spinosus L. – spiny amaranth

Subordinate Taxa

This plant has no children

Legal Status

U.S. Weed Information
Amaranthus spinosus spiny amaranth spiny amaranthus This plant can be weedy or invasive according to the authoritative sources noted below.This plant may be known by one or more common names in different places, and some are listed above. Click on an acronym to view each weed list, or click here for a composite list of Weeds of the U.S.
KY Haragan, P.D.. 1991. Weeds of Kentucky and adjacent states: a field guide . The University Press of Kentucky. Lexington, Kentucky.
SWSS Southern Weed Science Society. 1998. Weeds of the United States and Canada. CD-ROM . Southern Weed Science Society. Champaign, Illinois.

Wetland Status

Interpreting Wetland Status

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Caribbean FACU
Hawaii FACU
North America
Arid West FACU
Atlantic and Gulf Coastal Plain FACU
Eastern Mountains and Piedmont FACU
Great Plains FACU
Midwest FACU
Northcentral & Northeast FACU
Western Mountains, Valleys, and Coast FACU

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Jepson Interchange (University of California - Berkeley) (AMSP)
Lady Bird Johnson Wildflower Center Native Plant Information Network (AMSP)
Native American Ethnobotany (University of Michigan - Dearborn) (AMSP)
USF Atlas of Florida Vascular Plants (AMSP)
University of Tennessee Herbarium (Distribution) (AMSP)
University of Wisconsin - Stevens Point Freckmann Herbarium (AMSP)



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FNA | Family List | FNA Vol. 4 | Amaranthaceae | Amaranthus

20. Amaranthus spinosus Linnaeus, Sp. Pl. 2: 991. 1753.

Spiny amaranth, thorny amaranth

Plants glabrous or sparsely pubescent in the distal younger parts of stems and branches. Stems erect or sometimes ascending proximally, much-branched and bushy, rarely nearly simple, 0.3-1(-2) m; each node with paired, divergent spines (modified bracts) to 1.5(-2.5) cm. Leaves: petiole ± equaling or longer than blade; blade rhombic-ovate, ovate, or ovate-lanceolate, 3-10(-15) × 1.5-6 cm, base broadly cuneate, margins entire, plane or slightly undulate, apex acute or subobtuse to indistinctly emarginate, mucronulate. Inflorescences simple or compound terminal staminate spikes and axillary subglobose mostly pistillate clusters, erect or with reflexed or nodding tips, usually green to silvery green. Bracts of pistillate flowers lanceolate to ovate-lanceolate, shorter than tepals, apex attenuate. Pistillate flowers: tepals 5, obovate-lanceolate or spatulate-lanceolate, equal or subequal, 1.2-2 mm, apex mucronate or short-aristate; styles erect or spreading; stigmas 3. Staminate flowers: often terminal or in proximal glomerules; tepals 5, equal or subequal, 1.7-2.5 mm; stamens 5. Utricles ovoid to subglobose, 1.5-2.5 mm, membranaceous proximally, wrinkled and spongy or inflated distally, irregularly dehiscent or indehiscent. Seeds black, lenticular or subglobose-lenticular, 0.7-1 mm diam., smooth, shiny.

Flowering summer-fall. Waste places, fields, roadsides, railroads, barnyards, overgrazed pastures, other disturbed habitats; 0-700 m; introduced; Man., Ont.; Ala., Ark., Calif., Conn., Del., D.C., Fla., Ga., Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Minn., Miss., Mo., Nebr., N.J., N.Y., N.C., Ohio, Okla., Pa., R.I., S.C., Tenn., Tex., Vt., Va., W.Va., Wis.; Mexico; West Indies; Central America; South America; introduced nearly worldwide.

Amaranthus spinosus is native to lowlands in tropical America; at present it is a pantropical weed that also occurs in some warm-temperate regions.

Amaranthus spinosus, or its ancestral taxon, probably gave rise to the allopolyploid A. dubius by hybridization with some species of the A. hybridus aggregate (see above). Section Centrusa probably occupies a basal position, at least for the clade of subg. Amaranthus sect. Amaranthus, and probably for some representatives of subg. Acnida as currently outlined. Recent results of sequencing the ITS region (including ITS-1, 5.8S rDNA, and ITS-2) of nuclear ribosomal DNA from 15 species of Amaranthus occurring in China also suggest the basal position of A. spinosus among the studied species (Song B. H. et al. 2000). These results also confirm a profound divergence between subgenera Amaranthus and Albersia ; the latter is called "sect. Paucestamen " by the above authors. Data on the electrophoretic variation of seed proteins (R. H. Sammour et al. 1993) are also in accord with the segregation of these two subgenera; in the cited article, these groups are called sect. Amaranthus and sect. Blitopsis .


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