Having grown both of these plants for well over two years now, here are the differences from a hobbyist. The flowers on Hoya yvesrocheri are larger the corolla opens fuller then on H. stenophylla. The flowers are pink on H. yvesrocheri and yellow on H. stenophylla. The leaves on H. yvesrocheri are approximately three times the width as the leaves on stenophylla. Finally H. stenophylla is a far more vigorous grower than H. yvesrocheri.