I'm growing Poinsettia amaranth. I noticed "weeds" in my yard that look identical just in plain green and the flowers are similar just not in color.

Young plants almost have that line in the leaves like clover do to form a pattern.

Will they hybridize, and if pigweed survives here does that mean my ornamental amaranth will self seed all over my yard?

I think you are referring to Amaranthus palmeri which is called pigweed in my area, but more commonly called 'Carelessweed'. Also commonly called pigweed is Portulaca oleracea which is a type of purslane. I think your question is a good one. I've wondered if the domestic garden types of Amaranthus would hybridize with the native weed types but don't know the answer.

Yes, I think I have the red root pigweed growing wild here.

No idea where it came from as seedlings are everywhere, my guess is in birdseed.

There are a few "weedy" type Amaranthus commonly called Pigweed, these two in the database have photos:
Prostrate Pigweed (Amaranthus albus)
Redroot Pigweed (Amaranthus retroflexus)

There's a beautiful ornamental Amaranthus, commonly called Summer Poinsettia that is a perennial in warmer zones and acts as an annual in colder climates. Amaranthus tricolor: http://garden.org/plants/searc...

I don't know if cross pollination could occur between the weedy variety and the ornamental variety of Amaranthus or how long seeds are viable for any Amaranthus; I'd think they'd need warmth for germination.

Keith,
Yes and yes.

'Weedy' Amaranthus are varied natives across North America; A. retroflexus is quite ubiquitous
Several years ago I started with one 'Red Garnet' amaranth plant--it seeded itself all over my yard, and its progeny have done the same.
Every year it is a surprise where they will come up and what they will look like.
This was a 2013 garden hybrid


Here are some pics from this year

I usually pull the green ones, but I let this one go and it has purple flowers

The green one and the red one in this pic (click to enlarge) both came from the same seed head sowed here last fall.
They are obviously cross-pollinating with something else.

dirtdorphins said:Keith,
Yes and yes.

'Weedy' Amaranthus are varied natives across North America; A. retroflexus is quite ubiquitous
Several years ago I started with one 'Red Garnet' amaranth plant--it seeded itself all over my yard, and its progeny have done the same.
Every year it is a surprise where they will come up and what they will look like.
This was a 2013 garden hybrid

• Amaranth (Amaranthus)
• Uploaded by dirtdorphins

Here are some pics from this year

I usually pull the green ones, but I let this one go and it has purple flowers

The green one and the red one in this pic (click to enlarge) both came from the same seed head sowed here last fall.
They are obviously cross-pollinating with something else.

Thank you for sharing the photos! The purple one is so unique you should try and get more so it's not lost.

I'm keeping mine in area that gets weeds so the seeds drop and I'll see if they survive winter and sprout in spring.

Thanks Keith!
I thought it was a neat variation
We'll see what the bees come up with next year