Floral display in Narcissus: variation in flower size and number at the species, population, and individual levels

• Published in: International journal of plant sciences Vol. 161; no. 1; pp. 69 - 79
• Main Authors: Worley, A.C, Baker, A.M, Thompson, J.D, Barrett, S.C.H
• Format: Journal Article
• Language: English
• Published: United States The University of Chicago Press 2000; University of Chicago, acting through its Press
• Subjects: Biology; bulbs; diameter; flowers; Flowers & plants; genetic variation; measurement; Narcissus; phenology; Plant growth; Plant reproduction; pollinators; population; seed productivity; seed set; sexual reproduction; size; species differences; France; reproductive biology; ecology; resource allocation; flowering phenology; plant size; Amaryllidaceae; size-number trade-offs
• ISSN: 1058-5893; 1537-5315
• DOI: 10.1086/314225

Floral display (the size, number, and arrangement of open flowers)
influences pollinator visitation to animal-pollinated plants and
should be an important determinant of reproductive success. We examined
variation in the size and number of open flowers in wild daffodils
(Narcissus). Our analysis of published data on 45 taxa showed
that flower number varied negatively with flower diameter among
Narcissus species, which supports the widespread assumption
that there is a trade-off between these traits. In contrast, field
measurements indicated a positive relation between flower number and
diameter within two populations of Narcissus dubius, and no
relation was evident after we controlled for variation in bulb size. The
discrepancy between inter- and intraspecific patterns may have
occurred because variable resource levels obscure trade-offs when
variation in flower size is low (e.g., within species).
Size-related increases in floral tube length were half as great as
corresponding increases in flower diameter, a result that is consistent
with stronger stabilizing selection on tube length. Staggered flowering
within N. dubius inflorescences limited the mean number of
open flowers to <66% of total flower number, and slow expansion by later
opening flowers resulted in significant differences in flower size
throughout flowering. Although pollinators preferred large flowers,
experimental reductions in flower diameter did not affect seed production.
Our results illustrate how the relative importance of the
factors influencing floral display can vary among levels of biological
organization. Interspecific variation in flower size and number appeared to
be constrained by allocation trade-offs, but intraspecific variation
in both traits was more greatly influenced by plant resource status. Within
plants, the size and number of open flowers reflected the relative age of
individual flowers and floral longevity.