home | index | plant lab home | species directory
FNAI plant book | Atlas of Florida plants | Shirley Denton's plants of Florida photos

Asimina obovata (Annonaceae) (Willdenow) Nash
Common Name: Flag pawpaw, bigflower pawpaw

Distribution: Asimina obovata is endemic to central and south Florida, ranging from the northeastern to the southeastern peninsula (Nelson 1996). It is not a listed species.

Habitats: Asimina obovata is common in coastal dunes, dry sand ridges, sand pine scrub, pine flatwoods, scrubby flatwoods, and southern ridge sandhill (Abrahamson et al 1984, Nelson 1996). It prefers well-drained sand (Kral, 1960).

Life History: Asimina obovata is a deciduous, perennial, nonclonal aromatic shrub or small tree, to 1-3 m tall.Like other pawpaws, its stem architecture branches alternately and regularly in one plane (Kral 1960). Reddish pubescence conspicuously covers the young twigs, petioles, veins on lower surfaces of leaves, buds, and peduncles of A. obovata, distinguishing it from other pawpaws (Nelson 1996, Taylor 1992). Its leaves are yellow green to deep green, alternate, simple, entire, 4-12 cm long, 2-4 cm wide, leathery, and oblanceolate to oblong (Nelson 1996). The flowers are 6-10 cm broad, nodding, showy, and terminal on reddish hairy peduncles (Kral 1960). The calyx consists of three sepals. The corolla has six petals: three outer and three inner petals that are smaller than the outer petals by one half to a third (Zomlefer 1989, Norman 1986). Flower petals are initially green, but turn white or greenish white at anthesis. The inner petals have thick corrugated tissue on the bottom third of the inner surface of the petal (Norman 1986). This tissue turns deep maroon at flower maturity. Flowers become increasingly fragrant at maturity (Norman 1986). The androcium is globular, 0.5-1 cm broad, of numerous laminar stamens spirally arranged on the raised receptacle, forming a tight ring around the carpels. The stamens are pale green to beige at anthesis. Pollen is clustered in columns along the stamens and is released in tetrads. The gynocium averages five carpels; ovary superior; 1-loculed; ovules numerous (Zomlefer 1989). Fruits are large, yellowish green, ellipsoid, irregularly bulging, fleshy berries, usually clustered, 5-9 cm long, typical of the pawpaws (Nelson 1996). Seeds are brown at maturity, 1-2 cm long, in two irregular rows (Kral 1960)

Phenology: A. obovata flowers from March to May, typically for six weeks (Norman 1986). Flowers emerge after leaves have started to appear and have a basipetal sequence of bloom. Not all plants flower every year. In almost all flowers, pollen is not shed until stigmas turn brown. Then it is available for an average of one day (Norman, 1986). Anthers start to dehisce in the morning, but dehisce later in the day on colder days. The stigmas are shiny during the receptivity phase, generally 4-6 days. Fruit take 3-4 months to mature and eventually abscise from the plant. It is unknown how seeds are dispersed. Gopher tortoises were reported  (Kral 1960) to consume the fruit of A. pygmaea. Small mammals may help in the dispersal of Asimina obovata seeds although no studies have reported this. Seedlings are found extremely rarely.

Breeding System and Pollination: Asimina obovata is protogynous and xenogamous. Autogamy rarely occurs because of almost complete dichogamy. Fruit is initiated in hand-selfed flowers showing self-compatibility. This is consistent with most of the Annonaceae (e.g., Bawa et al. 1985; Bernhardt and Thien 1987) and with Asimina parviflora (Norman et al. 1992). Fruit initiation levels of hand-cross are marginally significantly higher than hand-self. Higher levels of early fruit abortion in hand-selfed than hand-crossed flowers suggests that there may be some inbreeding depression. Significantly higher levels of fruit initiation in cross versus open pollination indicate that it is pollinator limited. The Annonaceae family is primarily beetle pollinated (Gottsberger 1988). Beetles are the primary pollinators of Asimina obovata . Pollinators found by Norman et al, (1986) in Ocala National Forest, Volusia, and Marion counties were: Typocerus zebra (Oliv.)(Cerambycidae), Trichotinus rufobrunneus (Csy.), T. Lunulatus (Fab.), and Euphoria sepulchralis (Fab.) (Scarabaeidae). A study conducted at Archbold Biological Station found all of the above pollinators, but abundances differed from Norman’s study (Mathias 2002). Euphoria sepulchralis was only found once but was carrying pollen. Species found at Archbold were considered pollinators if they carried pollen >50% of the time and if they were found at least five times. Notolomus basilis (Curculionidae) occurred in large numbers and carried pollen over 50% of the time. However, Notolomus basilis is probably not one of the primary pollinators of Asimina obovata due to its very small size and small amounts of pollen carried (Matthias 2002). Beetles eat the corrugated tissue, nectar present at the base of inner petals, and pollen in A. obovata flowers (Norman 1986, Wood 1958)

Genetics: Hybrids of A. obovata have been observed with A. triloba (Zimmerman 1941), A. pygmaea (Norman 1986), and A. reticulata (Kral 1960).

Population Dynamics: A. obovata resprouts following fire with increased numbers of stems than were present pre-fire. Plants are typically vegetative the year following fire, but flower numbers in the second flowering season post-fire are higher than pre-fire levels. Herbivory of stems is increased in the first year post-fire as the stems are smaller and less woody. Flowering declines with time since last fire. Mortality rates are fairly low (< 10% annually) whether plants are burned or unburned.

Interesting Facts: The fruit of all Asimina species is edible (Zomlefer 1989), however, mature fruits of Asimina obovata are hard to find. This may be due to a combination of factors such as: pollinator limitation (Norman 1986, Matthias 2002), very high early abortion rates of initiated fruits, resource limitation, fruit parasitism, and removal of fruits by animals once on the ground. The common name pawpaw, derives from a corruption of the name for the tropical fruit tree papaya (Nelson 1996).

Data Collected by Archbold Biological Station’s Plant Ecology Lab: We collected demographic data from a single macrosite beginning in 1993 (but with two years missing) to the present. About half the plants in our study area were burned in 1996 and all study plants were burned in 2001. We record the number of stems and the number of stems suffering herbivory at several times each spring from February through June. Twice we also measured the basal diameter and height of each stem. Based on multiple visits at about 2-4 week intervals, we also determine the peak number of flowers, peak numbers of fruit and fruitlets initiated, matured, and parasitized. The total sample size is 331 plants in 29 patches. The lab conducted a seedling germination trial in scrubby flatwoods. A more detailed study of pollination, breeding systems, and fecundity was completed during spring 2002 (Matthias 2002). We identified insect visitors and potential pollinators of Asimina obovata flowers in scrubby flatwoods and sand pine scrub in 3 time-since-fire classes (including the demography site burned in 2001). Pollinator visitation rates, fruit initiation, and fruit maturation were examined in relation to conspecific flowering plant and flower density, flower display, fire history. Fire history was tested using stem height and canopy height. Flowers were bagged and treated to determine the breeding system of the plant. Flowers were hand pollinated with pollen from nearby plants to find potential fruit set, hand-selfed to test for geitonogamy, bagged and left alone to test for autogamy, and marked but left unbagged to determine levels of open pollination.

Data Availability: not currently available.

Contact Person: Eric S. Menges

References: 

1. Abrahamson, W. G., Johnson, A. F., Layne, J. N., Peroni, P. A. 1984. Vegetation of the Archbold Biological Station, Florida: An example of the Southern Lake Wales Ridge. Florida Scientist. 47:4:209-249.

2. Bawa, K. S., D.R. Perry, J. H. Beach. 1985. Reproductive biology of tropical lowland rainforest trees. Sexual systems and incompatibility mechanisms. Amer. J. Bot. 72:331-345.

3. Bernhart, P., L. B. Thien. 1987. Self-isolation and insect pollination in the primitive angiosperms: new evaluations of older hypotheses. Pl. Syst. Evol. 156:159-176.

4. Gottsberger, G. 1988. The Reproductive Biology of Primitive Angiosperms. Taxon 37:630-643.

5. Kral, R. 1960. A revision of Asimina and Deeringothamnus (Annonaceae). Brittonia 12:233-278.

6. Matthias, M. 2002. Effects of density and fire history on pollination and fecundity in Asimina obovata (Annonaceae). Intern Report, Archbold Biological Station.

7. Nelson, G. 1996. The Shrubs and Woody Vines of Florida. Pineapple Press Inc., Sarasota, Florida.

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

9. Norman, E. M., K. Rice, S. Cochran. 1992. Reproductive biology of Asimina parviflora (Annonaceae). Bulletin of the Torrey Botanical Club 119(1):1-5

10. Zomlefer, W. B. Flowering Plants of Florida, A Guide to Common Families. Biological Illustrations, Inc., Gainsville, Florida.

Home | Top | Index