Some characteristics to assist in separating
Buttercup Winterhazel (Corylopsis pauciflora) and Spike Winterhazel (Corylopsis spicata).

 Character
 C. pauciflora  Buttercup Winterhazel
 C. spicata  Sike Winterhazel
 Plant habit   to 3 m high, spreading   to 3 m high, spreading
 Young shoots   glabrous (i.e., without hairs)   pubescent
 Leaves   to 6.5 cm long, glaucous beneath, veins to 9   pairs, petiole to 1.5 cm long   4-11 cm long, glaucous and downy beneath, veins 6-7   pairs, petiole 1-2.5 cm long, pubescent
 Inflorescence   3 × 1 cm, 1-5 flowers   6 × 1.5 cm, 5-12 flowers
 Flower   anthers light yellow, filaments white, styles   yellow   anthers brown, purple or red, filaments pink, styles green
 Fruit   glabrous, 6-8 mm diameter   pubescent, to 8 mm diam

         Based on The New Royal Horticultural Society Dictionary of Gardening, Vol. 1, page 733.

   Note: "A floriferous hybrid between C. spicata and C. pauciflora is in cultivation."  Dirr, 1998, p. 277.

Species reference: 
Corylopsis