Here is the list of differences between the two species taken from above paper as well as Flora of China. Unfortunately, however, most of these differentiating characters are microscopic and may not be available in photographs we have, but may help in future photography of specimens:

T. angustifolia                                                   T. domingensis

1. Leaf sheaths auriculate at tip                   1. Leaf sheaths taper into lamina

2. Upper surface of leaf with brown spots.    2. Brown spots absent

3. Male part of spike ca 8 cm                         3. Male part of spike 7-30 cm

4. Compound pedicels of female flowers       4. Compound pedicels of female

     slender with brown streaks                            flowers dark brown and stumpy

5. Perigonial hairs of female flowers              5. Perigonial hairs of female flowers

    shorter and below stigma                               as equal to stigma

6. Colour of Female flower bracts                  6. Colour of Female flower bracts

     dark brown                                                     translucent

7. Staminate bracts forked at apex                7. Staminate bracts laciniate

8. Anthers twisted after dehiscence               8. Anthers not twisted after dehiscence

9. Anther 1.3-1.8 mm long                             9.  Anther ca 1.4 mm long

10. Stigmas ca as broad as style                  10. Stigmas broader than styles

I hope this helps. I am attaching above cited paper.