Pollination of Philodendron solimoesense

Species description

Philodendron solimoesense A.C. Sm.(subgenus Meconostigma) is a hemi-epiphyte of terra firma or flooded (riverine) forests that can also be terrestrial on sandy soils (figure 1). Its dark green leaves are sagittate with a blade reaching up to 1 meter long and fifty centimeters wide, and with inflorescences developing from the base of each petiole. The large inflorescences (open spadices: 22-32 cm in length) develop one after the other during the reproductive phase, with 2-7 days separating the opening of two inflorescences on the same individual (figure 2). The spathe is green externally and white internally, and its surface is smooth. The pistillate flowers occupy the lower portion of the spadix and take up ~20% of the total length of the inflorescence, whereas the male flowers are located on the upper portion and occupy ~30% of the total length. In the median portion of the spadix, there is a prominent intermediate zone (~50% of the total length of the inflorescence) consisting of sterile male flowers (picture 3). This study was conducted in July 1998 in French Guiana.

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Fig. 1. The habitat of Philodendron solimoesense.


Fig. 2. Inflorescences of P. solimoesense.

Insects visiting the inflorescences

Tyloderma sp., a curculionid beetle, was observed on dozen occasions mainly on pollinated inflorescences. The adults pierced large holes in the outer surface of the spathe in order to feed, and small holes in which to lay eggs. The larvae completed their development in the inflorescence peduncle where they pupated. Dozens of easily visible black spots from resin spurs indicated which spathes had been attacked.

Various ants recorded on all individuals patrolled on the outer surface of the opened spathes or on the upper part of the spadix, but avoided entering into the spathes.

Among insects visiting the opened inflorescences, staphylinid beetles and orange mirids (Hemiptera) were recorded from the first afternoon of observation. Staphylinids (up to 150 individuals per inflorescence) fed on sterile male flowers situated in the middle part of the spadix. Also, groups of 20-30 larvae were found in closed and pollinated inflorescences. At dusk up to 10 stingless bees (Trigona spp.) per inflorescence were noted (Figure 3). Very active until nightfall (18:45), they foraged on the upper part of the spadix, but were unable to reach the sheltered pollen. We twice observed large, reddish reduvidae preying on miridae and trying to catch Trigona.

In the beginning of the night, numerous staphylinids and mirids were therefore present when the pollinators, dynastine beetles of the genus Cyclocephala, arrived at the inflorescences

During the second day, mirids, staphylinids and Cyclocephala were still present in the inflorescences, while 20 to 40 Trigona per inflorescence were attracted by the spadix in the evening, collecting mucilage and some pollen until nightfall. When inflorescences at the first and the second day stage of opening developed in close vicinity, Trigona avoided the former. In the latter case they interfered slightly with the pollination of the inflorescences as they have finish to forage when, at dark, the anthers released massive pollen chains.

Pollination

The spathes opened in the middle of the morning of the "first-day", revealing the spadix, and were wide-open during the afternoon with an extremely curved white spadix (about 45° towards the exterior, Figure 4). At this time, the spathes were internally white, the stigmas were dry and a slight odor emanated from the inflorescence.

In the late afternoon (18:00), the spadix began to become hot, producing a strong and unpleasant odor. The stigmas became moist, and seemed to be receptive. The arrival at the inflorescence of Cyclocephala either directly or in a zigzag pattern, corresponded with the maximum level of heat production of the spadix and the strongest emission of the unpleasant odor, just before 20:00. Of all the insects recorded inside the inflorescences, they were the only ones that transported pollen on their bodies. After landing, they crawled down the spadix, and rapidly reached the protected floral chamber around the female flowers (Figure 5). While crawling around on the female flowers, they achieved pollination and numerous copulations were observed. Three Cyclocephala species were recorded in the inflorescences: C. colasi (899 individuals); C. emarginata (6); and C. sexpunctata (4). Both latter species, found in only six inflorescences, appeared to be rare pollinators of P. solimoesense, at least during July in this geographical zone.

During the following day, the Cyclocephala, rather inactive, were shy and photophobic, remaining hidden in the protected floral chamber. They fed upon the sterile male flowers situated just above the female zone. In highly visited inflorescences, 25-30% of the sterile male flowers were consumed, while pollinator feces accumulated at the base of the inflorescence or were found stuck on the inner face of the spathe.

In the early afternoon of the second day, the internal upper half of the spathes produced yellow droplets. In the late afternoon, a brownish resin covered the inner surface of the spathes (Figure 6). The spadix produces some heat and at a close distance the characteristic unpleasant odor remained.

Then, during about 60 minutes, the spathes closes wrapping around the spadix, from the base to the upper parts (Figure 7). At this time, the anthers released massive pollen chains (Figure 8) that stuck on the resin-covered cuticle of the Cyclocephala and are partly eaten by the pollinators (Figure 9). The space available for the pollinators decreased, so that they were progressively expelled, and obliged to climb out (Figure 10). Once a dead female was found crushed at the base of the spadix. The Cyclocephala reached the upper part of the spathe before complete closure, and then flew away to another inflorescence producing heat, and emitting the unpleasant odor.


Fig. 3. Trigona spp. on the inflorescence.


Fig. 4. An inflorescence on the first day of opening.


Fig. 5. Cyclocephala colasi in the floral chamber on the receptive female flowers.


Fig. 6. Inflorescence (second day) with an erect spadice and secreting resin on the spathe.


Fig. 7. Closing of the spathe (note the burn marks on the spathe).


Fig. 8. Pollen dehiscence.


Fig. 9. Cyclocephala feeding on pollen (note the resin produced by the spathe).


Fig. 10. Closing of the spathe on the pollinators.

Floral Biology

The flowering process was a very characteristic 2-day event of beetle-pollinated flowers. Other adaptations recorded in P. solimoesense are: heat production plus emission of a strong odor; presence of a floral chamber where pollinators copulate and shelter during the day, protogynous inflorescences (stigma receptivity before pollen release), offering of food rewards (stigmatic secretions, male sterile flowers), and closure of the inflorescences with pollinators extrusion.

Similar pollination cycle by Cyclocephala species have been found in two other Philodendron species of the subgenus Philodendron: P. melinonii Brongn. ex Regel (Figure 11) and P. squamiferum Poepp. (Figures 12 and 13). The main difference is that the resin is produced by the upper part of the spadix (i.e. male flowers) instead of the inner face of the spathe (Figure 14).


Fig. 11. Cyclocephala sp. in the floral chamber of an inflorescence of P. melinonii.


Fig. 12. Inflorescence of P. squamiferum on its second day, secreting resin on the spadix (note the "rubbish" left by the beetles at the bottom of the floral chamber and the damage on the sterile male flowers (food rewards)).


Fig. 13. Cyclocephala tylifera in the floral chamber of P. squamiferum.


Fig. 14. Pollen dehiscence in P. squamiferum mixed with the resin.

For further information, you can read:

Gibernau M., Barabé D., Cerdan P and Dejean A. 1999. Beetle pollination of Philodendron solimoesense (Araceae) in French Guiana. International Journal of Plant Science 160 : 1135-1143. This Adobe Acrobat PDF is made available compliments of the University of Chicago Press. Copyright © 1999 by The University of Chicago. All rights reserved.

Gibernau M., Barabé D. and Labat D. 2000. Flowering and pollination of Philodendron melinonii (Araceae) in French Guiana. Plant Biology 2 : 331-334.

Gibernau M. and Barabé D. 2002. Pollination ecology of Philodendron squamiferum (Araceae). Canadian Journal of Botany 80 : 316-320.

Other References to Aroid Pollination Literature

This page was created by Scott Hyndman for the I.A.S. on December 3, 2002.