Floral Biology

Despite the abundance of Lecythidaceae in many neotropical forests little information has been gathered about the family's floral biology. Only recently (Jackson and Salas, 1965; Dias, 1967; Mori and Kallunki, 1976; Prance, 1976; Mori et al, 1978) have data been published on the subject .This chapter summarizes the information given in the aforementioned papers. Lists of insect visitors to the flowers of Lecythidaceae and of the vouchers of the species of the Lecythidaceae studied are provided in Mori et al (1978).

Because an understanding of the structure of the androecium of Lecythidaceae is necessary for an understanding of the family's pollination, this chapter should be read in conjunction with our discussion of the flower in Chapter IV, Part 4.

Prior to our studies, Jackson and Salas (1965) investigated the pollination of Lecythis elliptica H.B.K. (=L. minor Jacq.) cultivated outside its natural range in Puerto Rico. They collected 43 species of insects in 10 orders from its flowers and found that the primary pollinator was the female carpenter bee, Xylocopa brasilianorum (L.). Their experiments also demonstrated that L. elliptica is allogamous. Dias in 1967 made an unpublished study of the pollination of Bertholletia excelsa Humb. & Bonpl. His insect collection, which Prance examined in Belem, reveals that the principal pollinators are Euglossine bees.

Our studies (Mori and Kailunki, 1976; Prance, 1976; Mori et al, 1978) have demonstrated that:

1. at least several species of the family are allogamous;

2. bees are the principle pollinators of neotropical Lecythidaceae;

3. those species with the most zygomorphic flowers have the fewest stamens;

4. species with actinomorphic or zygomorphic, open flowers utilize pollen as an attractant and those with zygomorphic closed flowers utilize nectar;

5. increasing zygomorphy and reduction in stamen number are concomitant with nectar production;

6. species with more specialized flowers (i e more zygomorphic, with closed hoods, fewer stamens, and nectar) are visited by more specialized bees than those species with less specialized flowers;

7. a combination of factors operate to reduce interspecific competition for pollinators.

The following is a summary of our knowledge of the pollination biology of neotropical Lecythidaceae. We begin with Gustavia, which has the least specialized flowers, and end with Couratari, which has the most specialized flowers.

Gustavia has large, actinomorphic flowers with numerous stamens that are fused at their bases to form a staminal ring. The species of Gustavia which we have observed produce few flowers daily over relatively long periods and do not produce nectar. The flowers of different species may have no scent detectable by humans, a scent detectable only at close range, or a strong, sweet odor. In some species odor may be produced only during a specific time of the day. The actinomorphic, open flowers of Gustavia do not restrict the entrance of insect visitors. Consequently, a large variety of pollen-gathering bees have been observed visiting the flowers. The commonest visitors are species of Melipona and Trigona bees. Examination of the pollen loads of 14 bees visiting G. superba and one visiting G. hexapetala showed that the pollen on the bees was 100% that of the plant species being visited. The bees generally enter the flowers by flying directly into the center of the ring of stamens. However, a few land on the filaments and crawl over or through them into the center of the flower. The arched arrangement of the stamens over the ovary directs the pollinators towards the stigma. After gathering pollen the bees often push their way out between the filaments and become completely covered by pollen. Bagging and crossing experiments with G. superba have shown that it is allogamous (Mori and Kallunki, 1976).

Pollination data for the other genera of Lecythidaceae with actinomorphic flowers (Asteranthos, Grias, Allantoma, and Cariniana) are lacking, although one of us (Prance) has observed many bees of several species visiting the flowers of Cariniana legalis.

Species of Couroupita have an asymmetrical androecium with anthers on both the staminal ring and the hood appendages. The hood is not appressed to the staminal ring and therefore the androecium is open to all kinds of insects. In addition, Thompson (1921) has demonstrated that the hood pollen of C. guianensis, although identical in structure to that of the staminal ring, is much larger. The larger pollen of the hood anthers may induce insects to collect pollen from there rather than from the staminal ring anthers. Comparative studies are needed of the hood and staminal ring pollen of all species of Lecythidaceae bearing the two types of stamens to determine if there are any structural and/or physiological differences between the pollen of the two.

Prance (1976) has previously described and illustrated the flowers of C. subsessilis. He also reported flower visits to this species by five species of wasp (Polybia flavitincta Fox, P. rejecta (F.), P. sericea (Oliver), Synoeca virginea (F.), and Chartergus sp.) and by honey bees (Apis mellifera L.) of the African variety. However, because wasps are not generally known to collect pollen and because C. subsessilis does not produce nectar, we are uncertain of the role wasps play in pollination. They may have been frequenting the flowers to prey upon other flower visitors.

More recently, we have collected Trigona dallatoreana Friese, T. capitata Smith, and T. pallida Latreille as they collected pollen from C. subsessilis (Mori et al, 1978). During an hour's observation the flowers of this species and closed hoods, fewer stamens, and nectar, e g species of Eschweilera and Couratari) are pollinated by bees with enough strength to force the hood open and with tongues long enough to reach the nectar at the apex of the coiled hood (e g Euglossine bees). Other species of Lecythidaceae with zygomorphic closed but uncoiled hoods may be mainly pollinated by robust bees without long tongues (e g species of Xylocopa).

Finally, we believe that certain mechanisms have evolved to insure that the pollinator(s) of a species of Lecythidaceae visit individuals of the same species consecutively, i e to insure floral constancy. Different species of Lecythidaceae appear to partition pollinator resources by: 1) occupying different habitats; 2) occupying different strata in the forest; 3) blooming at different times of the year; 4) having different flowering strategies (i e mass vs steady-state flowering); 5) having different floral structures adapted for different pollinators, and 6) offering either pollen or nectar as the pollinator at-tractant. Mori et al (1978) discuss these mechanisms in more detail.

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