I recall reading somewhere that Triumph was on of the few marques that used rosewood. I also assume that was on the early cars. The later cars do seem to be walnut and often quite plain grain, nice enough if it is finished right and in keeping with the style of the period.
Not always easy to do. I've seen quite a few otherwise spectacular restorations of high end cars like Jags, Bentleys and Rolls with woodwork that looked like it came out of my high school shop class. There are fine lines between elegance, simplicity and pretentiousness.
Tom