Species from, you've guessed it Texas! Originally called Clematis coccinea and often affectionately called the "Scarlet Lady" by clematis growers, it is herbaceous in habit in the UK with the stems dying down to ground level each winter. Clematis texensis is hardy and it will bear its small scarlet flowers from July to first frosts but prefers a sunny location. Never huge (it is unlikely to exceed 3M) it is nearly impossible to produce from cuttings and seed production is erratic in the UK, which is why it is often difficult to obtain.
The species was first described in 1850 and introduced to Europe by Max Baden-Baden.