Bigflower Pawpaw (MatBio: TREES & SHRUBS - Matanzas Biodiversity)

Bigflower Pawpaw

Asimina obovata

Summary ⁶

Asimina obovata, the bigflower pawpaw, is a shrub or small tree in the custard apple family. It is an endemic native to Florida, where it is found on open sandy hammocks and in dry woods. Showy white flowers in late winter to early summer are followed by large green edible fruit. Along with the other members of the genus, it serves as a host plant for zebra swallowtail butterfly and pawpaw sphinx moth

General description ⁷

Asimina obovata grows in the well-drained sands of coastal hammocks and dunes, sand ridges, and disturbed scrub habitats (Kral 1960: 253) (Norman & Clay 1986: 16). A long taproot may be a strategy to survive in xeric scrub habitats (Crummer 2003: 22).Asimina obovata is a perennial shrub that grows to a height of 2-3 m, with broad leaves and large flowers that are approximately 6 cm in width (Crummer 2003: 2). Asimina obovata flowers bloom in April (Norman & Clayton 1986: 18).

Asimina obovata protects itself from herbivores with a special toxin called annonaceous acetogenins (Lewis et al. 1993). This toxin inhibits the mitochondria’s ability to go through the process of respiration in the organism that consumes it (Crummer 2003: 2).

Crummer (2003) studied Asimina obovata in Ocala National Forest, Florida. Sun plants were found in <60% canopy and shade plants in >70% canopy (Crummer, 2003: 7). Mean specific leaf area of sun plants were larger (0.0093 m2 g-1 dry leaf tissue and shade plants ≈ 0.0150 m2g-1 dry leaf tissue (Crummer 2003: 29). Mean photosynthetic capacity of plants grown in 100% sun was greater than for plants in 31% sun and 7% sun, 16 µmol CO2 m-2 s-1, 11 µmol CO2 m-2 s-1, 10 µmol CO2 m-2 s-1, respectively (Crummer 2003: 11, 22, 30).

Seedlings grown in full sun had 19 µmol CO2 m-2 s-1 (Crummer 2003: 22-23). Normally, seedlings exposed to more than 31% of sun exposure do not have more photosynthetic capacity (Crummer 2003: 23). Having photosynthetic capacity in full sun may help prevent photodamage (Crummer 2003: 26-7). High-light tolerance enables seedlings to survive in open areas following fires (Crummer 2003: 27).

Pollination in A. obovata is through entomophily, which is the transfer of pollen by insects such as beetles.A. obovata emits a pleasant fragrance that grows stronger as the flowers mature (Norman & Clayton 1986: 18). Pollen is available for one day (Norman & Clayton 1986: 18). Beetles such as Typocereus zebra, Trichiotinus rufobrunneus, T. lunulatus, and Euphoria sepulchralis have been observed to visit A. obovata (Norman & Clay 1986: 18). Pistillate flowers had fewer visitors (27 beetles) than staminate flowers (75 beetles) from one study (Norman and Clayton 1986: 20). Typocereus zebra was the most common beetle visitor (Norman & Clayton, 1986: 20). Beetles feed on pollen and also on the carbohydrate-rich (50% of dry weight) inner petals (Norman & Clayton 1986: 17, 21).

A.obovata tend to have large (5-9 cm) fruits that are yellowish green when ripe, after 3-4 months (Kral 1960: 253; Norman & Clayton 1986: 20). Seeds are brown and 1-2 cm in length (Krall 1960: 253). Eight percent of flowers developed fruits and may be due to low visitation rates by beetles of the pistillate flowers and successful pollen transfer (Norman & Clayton 1986: 21-22). Any danger to the pollinating beetle species would have significant impacts on A. obovata due to the fact that relies on cross pollination and has extremely low survival rate with self-pollination.

References

Crummer, K. G. 2003. Physiological leaf traits of scrub pawpaw, Asimina obovata (Willd.) Nash (Annonaceae).M.Sc. thesis dissertation, University of Florida. 55 pages.

Kral, R. 1960. A revision of Asimina and Deeringothamnus (Annonaceae). Brittonia 12.4: 233-278.

Lewis, M.A., Arnason, J. T., Philogene, B. J. R., Rupprecht, J. K., & McLaughlin, J. L. 1993. Inhibition of respiration by asimicin, an insecticidal acetogenin of the pawpaw, Asimina triloba (Annonaceae). Pesticide Biochemistry and Physiology 45: 15- 23.

Norman, E. M. & Clayton, D. 1986. Reproductive biology of two Florida pawpaws: Asimina obovata and A. pygmaea (Annonaceae). Bulletin of the Torrey Botanical Club 113: 16–22.