Some help would be appreciated

[outplayed]

I found these Three at a shop in Saudi Arabia

First one:
Length: 16"







Second one:
Length: 4"to 14"









Third one:
Length: This one was very tall, although not in very good health 30"+

[Kamos]

#1 Myrtillocactus geometrazens
#2 Pachycereus marginatas

[hegar]

I agree on those first two with Kamos:

1. M. geometrizans
2. P. marginatus

Both are large, columnar, fast-growing cacti.

Harald

[SnowFella]

Wouldn't call M. geometrizans columnar, mine's more of a bush than straight up stem

[DaveW]

I suppose you could call mature M. geometrizans both columnar and bushy. I think ramose would be the better term:-

http://www.wordreference.com/definition/ramose" onclick="window.open(this.href);return false;

http://commons.wikimedia.org/wiki/File: ... 04_ies.jpg" onclick="window.open(this.href);return false;

[jfabiao]

The last one looks like Acanthocereus tetragonus.