DIASPORE MORPHOLOGY AND SEED DISPERSAL IN SEVERAL WIND-DISPERSED ASTERACEAE

Area of Science:

• Plant dispersal biology
• Evolutionary morphology
• Aerodynamics of seeds

Background:

• Wind-dispersed seeds (diaspores) rely on aerodynamic properties for dispersal.
• Understanding the relationship between seed morphology, plume loading, and settling velocity is crucial for plant ecology.
• Previous models often rely on Stokes' Law, which may not apply to all seed types.

Purpose of the Study:

• To investigate the relationship between seed morphology, plume loading, and settling velocity in wind-dispersed Asteraceae.
• To evaluate the applicability of Stokes' Law in predicting seed settling velocity.
• To explore the evolutionary implications of seed traits for dispersal ability.

Main Methods:

• Morphological measurements of seeds from 19 wind-dispersed Asteraceae species.
• Calculation of Reynolds numbers and approximate plume loadings for each species.
• Measurement of diaspore settling velocities.

Main Results:

• Diaspore settling velocity showed a linear increase with the square root of plume loading.
• Beaked achenes exhibited significantly lower settling velocities than unbeaked achenes, despite similar plume loading and Reynolds numbers.
• Reynolds numbers were generally above the range where Stokes' Law is applicable, indicating its limitations for these seeds.

Conclusions:

• The study recommends limiting the use of Stokes' Law-based formulas for seed settling velocity predictions in similar contexts.
• Seed characters, including beak presence, may have evolved under selection pressure favoring enhanced dispersal.
• Observed relationships suggest a balance between evolutionary selection for dispersal and morphological constraints within plant families.