Questions about watercress

[Guest guest]

Hi;

Please excuse the ignorant questions. I never started eating

vegetables until I was teenager and then rarely ever salad greens.

I was poking around this site and discovered that watercress is about

1/2 the calories of lettuce as well as have almost 3 times the calcium:

http://www.nal.usda.gov/fnic/foodcomp/search/

Aside from a tiny, expensive package of organic watercress I bought at

a co-op this past weekend I have never seen watercress.

How absorbable is the calcium in watercress?

Is it a high or low oxalate vegetable?

Do regular supermarkets ( in the USA ) carry watercress? Is it

expensive ( the head of lettuce I tried was $1.99 a head )? Do people

eat the stems? Is there much nutritional value in the stems?

Thanks in advance for any info

Steve