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Fruit On Alula Plant At Palomar College Polynesian Garden
© W.P. Armstrong 8 December 2021
       Alula Image Page 1       Alula Image Page 2  

  Polynesian Garden On Campus Of Palomar College  
On 8 December 2021, I photographed an alula plant (Brighamia insignis) with developing seed capsules. In order to set fruit it was undoubtedly pollinated, but the pollinator remains a mystery. Unlike other seed-producing alula plants on campus, it was not hand-pollinated. In its natural habitat on the steep cliffs of Kauai, alula can no longer produce seeds because its native pollinator moth is now extinct. Some authors have suggested that its pollinator is the very rare & endangered green sphinx moth (Tinostoma smaragditis), rediscovered in eastern Kauai in 1998. In the wild, alula was apparently pollinated by long-tongued hawkmoths through outcrossing (cross pollination). Luckily alula responds well to hand pollination. Like the California condor, this unique species has been brought back from the brink of extinction through breeding programs.

The Following 2 Images Of Alula Fruit Were Taken 8 Dec. 2021:

Developing fruits (seed capsules) on alula plant in Palomar College Polynesian Garden (8 Dec. 2021). A white, milky latex-like material has exuded from the longitudinal slits. Members of the bellflower family (Campanulaceae), to which Brighamia belongs, commonly produce a milky latex. This plant was not hand-pollinated

According to T.G. Lammers (1989), the flowers of alula are protandrous. This means that the anthers mature and release pollen before the stigma is receptive, a plant strategy favoring cross pollination. At Palomar College, do visitations by native bees and possibly night-flying moths provide sufficient pollen transfer and fertilization for the large number of ovules in alula ovaries? The bottom line here is how does an alula flower set seed in the Polynesian Garden without hand pollination? In other words, who is pollinating it? Is it self-pollinated by some unknown mechanism? Seana Walch of the National Tropical Botanical Garden reported a self-pollinated alula flower (bagged in bud and left unmanipulated) that set fruit with viable seeds (personal communication, 2019).

On 16 Nov 2019 at 12:00 noon I spotted a small, black, solitary flower bee on an alula flower in the Palomar College Polynesian Garden. I originally thought it was in the family Megachilidae, but according to Karl Magnacca at University of Hawaii, it belongs to the genus Lasioglossum in the family Halictidae. Bees in this family are important pollinators in San Diego County, particularly the Anza-Borrego Desert region. This bee was definitely interested in the alula flower and was in the apex of floral tube collecting pollen grains from the anther column and from corolla throat. I collected the bee and flower and placed them in a closed vase with water for observations. I watched the bee move about on the flower and it appeared mostly interested in the pollen-bearing anther column; however, after several days it landed several times on the stigma.

The images for this collage were taken from the following Wayne's Word alula image pages 1 & 2. Regarding the natural pollination of alula in the Polynesian Garden at Palomar College, my hypothesis is that wild flower bees, and possibly other insects are possible pollinators of this remarkable Hawaiian native. At least some pollen tubes may reach the alula ovary and fertilize some of the numerous ovules. My hypothesis is solely based on my observations and images and has not been thoroughly tested. As I stated above, do visitations by native bees provide sufficient pollen transfer to account for the large number of seeds observed in alula plants on campus?
       Alula Image Page 1       Alula Image Page 2  

Longitudinal section of ovary. Fertilized ovules develop into seeds.

Mature seed capsules & minute seeds of alula (Brighamia insignis).

Alula seed capsule from Palomar College Polynesian Garden. I counted approximately 300 seeds in this capsule. In another capsule I counted 273 seeds. I think it is safe to say that a conservative estimate for alula is 200 to 300 seeds per capsule based on plants in the Palomar College Polynesian Garden. They have endosperm tissue indicating that the original ovules were fertilized. Initially, my seed sample floated on the water surface, but after several days most sank to the bottom.

Germinating alula seeds from capsule on plant in Palomar College Polynesian Garden (4 Jan 2022). They have sprouted in Las Posas soil at my home in Twin Oaks Valley from soil dervived from iron/magnesium-rich San Marcos Gabbro. I scattered about 25 seeds on soil surface in this small bowl (4.5 inches in diameter) in late Dec 2021. This is too many seeds in such a small bowl; however, I incorrecty doubted their viability in this soil! In 14 days I counted 18 germinated seeds, a conservative percent viability of 72%.
More Germinating Alula Seeds:

More germinating alula seeds from capsule on plant in Palomar College Polynesian Garden. These are growing in my living room under Grow Light for indoor plants! The soil mix is from Palomar College Horticulturist Tony Rangel.

Are There Native Species In The Campanulaceae In San Diego County?

The answer is yes. In fact, there are a number of beautiful wildflowers in the same family as alula. One of these is the genus Nemacladus with 9 species, mostly in desert areas. Although the flowers are minute, they are quite beautiful when magnified in a macro image. Another is Downingia in a vernal pool field near Palomar College. It is in grave danger due to urbanization.

Did Any Alula Pollen Adhere To Flower Bee?

The flower bee (Lasioglossum) definitely picked up alula pollen on its hairy body and appendages. The above image shows alula pollen grains on compound eye and on fringe of hairs around mouth region below clypeus. There were also scattered pollen grains on its thorax and abdomen. I also observed tricolporate pollen grains on the hairy upper and lower surfaces of alula stigma. I compared them with pollen grains on anther column and they appeared to be from an alula flower, undoubtedly transferred by an insect! Note: In this image I have pushed my old Nikon D-90 (with macro lens + 3 extension rings) to the limits of its resolving power.

Tricolporate pollen from alula flower. The grains have a triangular shape with 3 furrows or grooves in the exine (outer layer of grain). Most of the grains in this image appeared viable (not empty or shrunken), but I did not test them with stains. Photographed through 100x objective on compound microscope and zoomed up to at least 200x magnification with Sony W300 digital camera. Note: Alula pollen tested with Alexander's stain by Beth Pearson of the Palomar College Life Sciences Department appeared magenta-red, indicating pollen viability.

References:

 Some Information on this page is sumarized from Wayne's Word (waynesword.palomar.edu), including Botanical Record-Breakers, Arboretum Newsletters and Flower Terminology.

 Johnson, S.D., & R.A. Raguso. 2016. "The Long-Tongued Hawkmoth Pollinator Niche For Native and Invasive Plants in Africa." Ann. Bot. 117 (1): 15-36. doi: 10.1093/aob/mcv137.

 Lammers, T.G. 1989. "Revision of Brighamia (Campanulaceae: Lobelioideae) a Caudiciform Succulent Endemic to the Hawaiian Islands." Systematic Botany 4 (1): pp 133-138.

 Wagner, W.L., D.R. Herbst, and S.H. Sohmer. 1999. Manual of the Flowering Plants
of Hawaii. Volume 1. University of Hawaii Press, Honolulu, Hawaii. 988 p.

 Walch, Seana. K. 2015. Floral Biology, Breeding System, Pollination Ecology, and Ex Situ Genetic Diversity of the Endangered Hawaiian Species, Brighamia insignis A. Gray (Campanulaceae). A Thesis Submitted to the Graduate Division of the University of Hawai'i at Manoa in Partial Fulfillment of the Requirements for the Degree of Master of Science In Botany. 102 p.

 Walch, Seana K., et al. 2019. Pollination Biology Reveals Challenges to Restoring Populations of Brighamia insignis (Campanulaceae),a Critically Endangered Plant Species From Hawai'i."
Flora 259: October 2019, 51448. https://doi.org/10.1016/j.flora.2019.151448

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