Hiya Trish! Thanks for dropping by the Clems forum! There is one evergreen already photographed in the database... Sweet Autumn, otherwise known as terniflora. The pictures are posted here:
http://cubits.org/Clematis/thr...
Terniflora is a wonderful performer... but sometimes TOO wonderful. It tends to reseed itself at will and can be very impolite to its neighbors. IMO it's not a good choice for an area where you want it to be mannerly and play well with others.
If you had asked this question in the fall, I would have wholeheartedly recommended crassifolia... but now that we have had extended periods of 17F weather here, my crassifolia is certainly not evergreen! I have one vine that is still green, but the rest turned crispy brown and promptly dropped their leaves. Crassifolia is an interesting cultivar because the leaves have white mottling on them... it provides a great visual interest even when the plant is not in bloom. But, after this year's rough winter, I'm not sure I can recommend it as an "evergreen" variety anymore!
Those are the only two evergreen clematis I have personal experience with, but I believe others in the Cubit may grow some they can chime in about. One I would really like to know more about is Apple Blossom, if anyone here has grown it. Here's a link to the info page for it on COTW:
http://www.clematis.hull.ac.uk.... It's rated for Zones 7-9 so it should do fine for you there in Texas.
Not that I don't love clematis... but have you considered a jasmine for that location? I have both Confederate (white blooms) and Carolina (yelllow blooms) jasmine growing at this house and both made it through our rough weather with flying colors... still green and beautiful. They both have long bloom periods and the flowers are very fragrant. I typically get multiple bloom periods with my Carolinas. For both of these plants, the vines will need pruning once a season to keep them in check, but I have never had them reseed into other areas... so I suppose I would call them mannerly with dreams of being thugs!!!
Hopefully someone else will chime in regarding their experience with evergreen clems!
Evey =)
