At least some Arisaema naturally die back some time between late spring and late summer. With this hot dry weather, I would guess that this tendency to be ephemeral may be speeded up.

So it is going dormant? Why only one stem is going yellow though? I have 2 more of the same arisaemas and they are not yellowing like this one. Also I thought this particular arisaema don't go dormant early? And the rate of yellowing from yesterday to today..isn't it a little too fast for trying to become dormant?

could it be chlorotic? I know nothing of this plant.

The oldest leaf is yellowing first. The others will follow. It's behaving absolutely normally. You'll be left with the spike of berries sticking up by itself.

As floral and babs said, it's time. Time does this to plants...they live, they go dormant, etc.

Mine are also going down here, in Lancaster PA. High temps, and no significant rain in 3 weeks, sped up the process, I believe. Just hoping they return next year ($$$)!

Oh so they really are going dormant this early.. so does the spike of berries stay up until frost?

Yes, and no.

Ok how long do they stay up until?

Just like the leaves, it depends on weather, soil moisture, critters (though I am not sure how many critters will eat these), sun exposure, etc. The wild native Arisaema in this area usually stay around until at least late summer, but that would be in shaded, consistently moist, organic soil for their growing conditions.

This will be a case of waiting to see how they do in the soil, light, etc that yours are in as well as the species. When they have been in that spot in your garden for 5 years you can tell us how long they last in your garden, though it will be an average that varies from year to year.

Sit back, enjoy and mark up the knowledge for next year. Next year it might act differently. Never know.

How come my 2 other of the exact arisaema not doing this? Still very green

Because they have different genes and they are in a slightly different spots and so may have difference in light water ,etc, etc. Relax and enjoy the fact that they are growing well. I seem to recall that early in the season you were convinced that one had rotted and it was fine. You can either make your garden a joyful experience or you can lose all that in worrying and looking for problems that aren’t there. Relax and enjoy.

Even the same exact plant can have different genes?

Yes, TC is vulnerable to early mutations as the cells proliferate.

Point of fact, African Violets (which can be vegetatively reproduced by leaf cuttings) very frequently are not identical to their progenitors. But then AVs tend to be genetically unstable anyway.

I see I see. I'm pretty sure they were divided through bulblets. Not 100% sure, they are from this nursery that imports plants from Japan so this arisaema itself was propagated in Japan. So maybe that is why one stem of this arisaema is red and the other two is yellow.

From your pictures, it appears that your soil could seriously use some mulch. Mulch will help maintain soil moisture, even out temperatures, and provide nutrients as it decomposes. Oh, it helps keep down weeds too.