Key to Amaranthus

View taxon page for Amaranthus

(For a list of species in Amaranthus, use the above link.)

Jepson Manual glossary definitions can be seen by moving your cursor over words underlined with dots.

1. Dioecious

2. Plant in hand pistillate

3. Perianth parts 1–2, 1 narrowly 

lanceolate 

Narrowly elongate, widest in the basal half, often tapered to an acute tip.

, 1 rudimentary or 0 ..... A. tuberculatus var. rudis (2)

3' Perianth parts 5, well developed, fan- or spoon-shaped

4. Bracts <= perianth parts ..... A. arenicola (2)

4' Bracts > than perianth parts

5. Plant ± glabrous; outer perianth parts ± 

acuminate 

Having a long-tapered, sharp tip, the sides concave.

..... A. palmeri (2)

5' Plant glandular-hairy especially on bracts; outer perianth parts 

obtuse 

Having a short-tapered, blunt tip or base, the sides convex or straight and converging at more than a right angle.

to ± notched, mucronate ..... A. watsonii (2)

2' Plant in hand staminate

6. Bracts <= 2 mm ..... A. tuberculatus var. rudis (2)

6' Bracts (1.4)2–6 mm

7. Outer perianth parts acuminate, spine-tipped; bracts >= perianth parts ..... A. palmeri (2)

7' Outer perianth parts mucronate; bracts <= perianth parts

8. Inflorescence axis and bracts glabrous ..... A. arenicola (2)

8' Inflorescence axis and bracts generally sparsely glandular-hairy ..... A. watsonii (2)

1' Monoecious

9. Nodes with 2 spines ..... [A. spinosus]

9' Nodes without spines

10. Perianth parts 1–3, only 1 well developed ..... A. californicus

10' Perianth parts (2)3–5, all well developed.

11. Pistillate perianth parts fan-shaped, margins 

fringed 

Having ragged or finely cut margins.

or finely 

dentate 

Having margins with sharp, relatively coarse teeth pointing outward, not tipward.

..... A. fimbriatus

11' Pistillate perianth parts not fan-shaped, margins 

entire 

Having margins that are continuous and smooth (i.e., without teeth, lobes, etc.).

12. Inflorescence of 

axillary 

Pertaining to or within an axil, especially a leaf axil.

clusters only, or axillary and terminal

13. Perianth parts (3)4–5

14. Perianth parts narrow-ovate to 

oblong 

Longer than wide, with nearly parallel sides; wider than linear.

; seeds 1.3–1.7 mm ..... A. blitoides

14' Perianth parts narrow-spoon-shaped; seeds 0.9–1.1 mm ..... A. torreyi

13' Perianth parts (2)3

15. Fruit 

dehiscent 

Opening at maturity to release contents; usually pertaining to anthers or fruits.

; bracts 1.5–4 mm, tip ± spined ..... A. albus

15' Fruit 

indehiscent 

Not opening inherently to release contents; usually pertaining to fruits.

; bracts <= 1 mm, tip not spined

16. Stem hairy distally; fruit 2–3 mm, smooth ..... A. deflexus

16' Stem ± glabrous; fruit 1.2–1.5 mm, wrinkled

17. Leaf tip entire or ± notched; seeds dull, dotted ..... [A. viridis]

17' Leaf tip deeply notched to 2-lobed; seeds shiny, only margins dotted ..... [A. blitum subsp. emarginatus]

12' Inflorescence terminal only

18. Inflorescence green; bracts > stigma; seeds brown to black; often weedy

19. Perianth parts spoon-shaped to obovate, overlapping, 

reflexed 

Abruptly bent or curved downward or backward.

in age, tip rounded to ± notched ..... A. retroflexus

19' Perianth parts 

linear 

Elongate, with nearly parallel sides; narrower than elliptic or oblong.

to lance-oblong, not overlapping, 

erect 

Upright; vertically oriented.

, tip 

acute 

Having a short-tapered, sharp tip, the sides convex or straight and converging at less than a right angle.

to awned

20. Leaf blades rhombic-ovate or widely lanceolate; inflorescence of many thin, flexible branches; bracts 2–4 mm ..... A. hybridus

20' Leaf blades 

elliptic 

In the shape of a flattened circle or ellipse; wider than linear

, rhombic to widely lanceolate; inflorescence of few rigid, erect branches; bracts 4.5–6(8) mm ..... A. powellii

18' Inflorescence brightly colored, not green; bracts generally <= stigma; seeds white to ± red-brown or black; cultivated, rarely escaped

21. Inflorescence main axis generally drooping or nodding; perianth parts widely spoon-shaped, margins overlapping, tip obtuse to rounded ..... [A. caudatus]

21' Inflorescence not drooping or nodding; perianth parts linear to elliptic (obovate), margins not overlapping, acute to acuminate (rounded)

22. Inflorescence erect to flexible, lateral axes thin, flexible, 3–8(12) cm, 0.5–1 cm wide; bracts 1.8–2.5 mm; fruit tip abruptly narrowed to a beak ..... [A. cruentus]

22' Inflorescence erect, lateral axes thick, stiff, 9–20(30) cm, 1.2–2 cm wide; bracts 3–5(6) mm; fruit tip gradually narrowed ..... [A. hypochondriacus]

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