Book  (Oct 2001)  Page(s) 160-161.  Includes photo(s).

Book  (1996)  Page(s) 145.  
 
'Crepuscule' Also seen as C. x bonstedtii 'Crepuscule', this is said by Bean to be a hybrid between C. heracleifolia and C. stans, raised by Lemoine

Book  (1989)  Page(s) 90.  
 
Among Lemoine's many heracleifolia x stans crosses, 'Crépuscule' is one that survived, but something has re-entered growers' lists as 'Bonstedtii Crépuscule'. It has an altogether smoother leaf and more compact habit than C.

Book  (1951)  Page(s) 155.  
 
Clematis bonstedtii (Wehrh.). Crépuscule; Parent form from Northern China. Herbaceous, non-climbing Clematis. Foliage with three leaflets, large, light green. Numerous blooms, conical. Light blue. 100 cm. July-September. Propagation by slips.

Magazine  (Jul 1937)  Page(s) 106-107.  
 
Lemoine, de Nancy, a beaucoup amélioré cette espèce en croisant les C. Davidiana x C. Stans, nous y trouvons actuellement des fleurs à longs tubes, plus ou moins serrées sur la tige les variétés : Crépuscule, Comète, Campanule, Côte d'Azur, Ondine et autres ont des coloris bleu, blanc bleuâtre, mauve du plus joli effet. Ces plantes groupées, disséminées ou isolées en plates-bandes ou sur les pelouses sont très remarquées.

Magazine  (1931)  Page(s) 250.  
 
The late-flowering herbaceous Clematis heracleaefolia varieties Azur, Cyprius, Crepuscule and Oiseau Blue, are most effective, the blooms, produced in whorls, being in shades of blue, and very fragrant.