[Top] Double spiral arrangement of a C. asiaticum's umbel. The pedicellated umbels are spiral cymes which have coiled up and thus flower sequentially.
[Bottom] Single spiral arrangement of C. moorei umbel.
Note, sessile flowered Crinum have group arrangements for the buds where the bud-groups flower semi-sequentially. There is a distinct evolutionary separation between the two types.
According to Muller-Doblies and G. Ledyard Stebbins the pedicellated umbels like C. asiaticum and C. moorei are composed of cymes which originally resembled those of Gladiolus. These had coiled up to form a helicoid cyme, a 'determinate' type of umbel where the single pedicellated blossoms flower sequentially. In contrast, the sessile flowered umbels display group flowering. These umbels were derived from 'indeterminate' compound racimes where each distinctive bud group flowers sequentially. As noted by Herbert, the sessile flowered Crinum are essentially tropical in habitat while the pedicellated are subtropical. There is a distinctive evolutionary separation here which becomes evident on ones attempted selfing of interspecific hybrids like C. 'Ellen Bosanquet' or C. x herbertii where one parent is sessile and the other pedicellated.