Table 1.

Chromosome numbers, flowering type (D, dioecious; M, monoecious), fertilization type (O, outcrossing; S, primarily selfing), and previous reports of interspecific hybridization among selected Amaranthus species. F₁ hybrids known to occur (Y) or unknown whether hybrids occur (U)

	Flowering type and fertilization	Chromosome number (2n)*	Amaranthus palmeri	Amaranthus hybridus	Amaranthus powellii	Amaranthus retroflexus	Amaranthus spinosus	Amaranthus tuberculatus
A. palmeri	D, O	34, 32†	–	U	U	U	U	Y‡,§,¶,**
A. hybridus	M, S	32		–	Y††	Y††	Y††	Y††,‡‡,§§,¶¶
A. powellii	M, S	34			–	Y††	U	Y††
A. retroflexus	M, S	34				–	Y††	Y††
A. spinosus	M, O	34					–	Y††
A. tuberculatus***	D, O	32						–

^*Reported in Grant (1959c).

^†Reported in Rayburn et al. (2005).

^‡Wetzel et al. (1999b).

^§Trucco et al. (2007).

^¶Steinau et al. (2003).

^**Franssen et al. (2001b).

^††Murray (1940).

^‡‡Trucco et al. (2005b).

^§§Tranel et al. (2002).

^¶¶Trucco et al. (2005a).

^***A. tuberculatus includes former designations Acnida tamariscina, Acnida tuberculata, and Amaranthus rudis.