Agave americana 'Marginata'

Agave amerciana 'Marginata'
This plant differs from Agave americana only in having yellow leaf margins instead of the plain silver/green colour. There are many named forms of A. americana with different colours, patterns of stripes and forms of leaves. As well as the described forms, it hybridises easily making intermeadiate forms and sports. 

Left - This close up shows how the the leaves curl sometimes inward, when they are young. As they age and become less upright they straighten and then recurve downwards. 
Centre - this plant is growing in the Carribean Home From Home desert style planting, where it has survived 6 winters, sometimes with prolonged spells of very wet weather. It has experienced -8c for short periods and -6 lasting for a few days with the temperature hardly rising above 0c during daytime, without protection and sustaining only superficial damage.
Right - You can see that the leaves scar and catch on one another as the rosette throws out new leaves from the centre, forcing the old ones to relax gradually into horizontal positions.