The flower is very different from members of the lobelia family on the mainland of North America. Another rare species with white flowers (B. rockii) grows on sea cliffs along the windward coast of Molokai. Like Hawaii's endemic silver sword alliance that evolved from an ancestral tarweed (Asteraceae), the alula is another example of adaptive radiation. According to Sherwin Carlquist (Hawaii: A Natural History, 1980), the Hawaiian lobeliads evolved from several ancestral introductions rather than a single original colonization; however, molecular data from Thomas J. Givnish of the University of Wisconsin (Evolution on Islands, 1998) indicate that they are monophyletic in origin and represent the product of a single introduction.

In its native habitat, the blossoms of G. thunbergia are visited by nocturnal hawkmoths of the genus Agrius (family Sphingidae), similar to our western North American Manduca moths that pollinate jimsonweeds (Datura wrightii). They are called sphinx moths because the alarm posture of some larvae resemble the form of the Egyptian sphinx. Some hawkmoths have tongues (proboscides) up to 5.5 inches (14 cm) long (or longer), long enough to reach the plentiful supply of nectar deep within the floral tube. The proboscis roles up into a neat, compact coil when the moth is not feeding. When the proboscis is inserted into the floral tube, it passes through a ring of eight stamens which are heavily laden with pollen. Pollen adheres to the sticky proboscis and other furry body parts and is transferred to other flowers as the moths feed. Anthers of individual flowers mature and shed pollen before the stigma is receptive, a maturation sequence conducive to cross pollination. This maturation sequence is called protandry (1st + male).

The African hawkmoth (Agrius convolvuli) pollinates Gardenia thunbergia and at least 13 additional species with long corolla tubes, including Crinum, Gladiolus, Rangaeris, and Harveya (Johnson & Raguso, 2016). It seems entirely possible that our local hawkmoths (Hyles lineata and/or the longer-tongued Manduca sexta) could pollinate Gardenia thunbergia in San Diego County, although I suppose there could be other pollinators during daytime hours. It is interesting to note that the African moth Agrius has a Hawaiian relative, the pink-spotted hawkmoth (Agrius cingulata).

There is an extremely rare gardenia shrub (Gardenia brighamii) endemic to the Hawaiian Islands. According to the Hawaiian Native Plant Propagation Database, this species is self-compatible and viable seed is produced by self pollination. Another African species (G. volkensii) has night-blooming flowers and woody fruits like G. thunbergia and is presumably moth pollinated.

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. https://doi.org/10.1093/aob/mcv137

2. According to the Hawaiian Native Plant Propagation Database, when the flowers are a couple of days old, the pollen will begin being shed. Use a small paint brush to pick up pollen that has fallen onto the floral tube and apply the pollen to the stigma of "another" flower. The stigma is ready to receive the pollen when it appears shiny and sticky. By "another" flower, I assume they mean a different plant; however, I would like to try the same flower. I have seen ample pollen on the same flower with a receptive stigma.

3. On some of the above images there is abundant pollen on the bases of petals in flowers with receptive stigmas. Is this viable pollen? According to Tony Rangel, our alula plants came from seed from the San Diego Zoo (circa 2007-2009). The Zoo acquired their seed from NTBG (National Tropical Botanical Garden). Since the original plants on the cliffs of Kauai are so few in number, the genetic variability in the seed from hand pollinated plants is undoubtedly low. I originally thought our plants required cross pollination because they are protandrous (anthers release pollen before stigma is receptive); however, I am puzzled by pollen in flowers with receptive stigmas. Ideally, we should try hand pollination on our plants using pollen from same flower as receptive stigma.

4. Based on this dissected flower, slits (splits) in floral tube of alula flowers do not extend into the style. After pollination at the stigma, the pollen grain forms a pollen tube that grows all the way down the style into the ovary where the ovules are located. The pollen tube penetrates a tiny receptive ovule and injects 2 sperm cells. If double fertilization is successful this tiny ovule will develop into a seed. Each ovule must receive a separate pollen tube in order to develop into a seed. Unfertilized ovules simply abort.

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 Longitudinal view of alula ovary.

5. When a long-tongued hawkmoth inserts its long proboscis deep into the floral tube, it is rewarded with sweet, nourishing nectar produced by nectaries deep in the floral tube. The moth will undoubtedy get pollen on its hairy face in the process. On the arrival at another flower, possibly on a different plant, some of this pollen may be transferred to the sticky, receptive stigma exerted from the flower. This is cross pollination. Whether this event can occur on alula plants with native hawkmoths of San Diego County is unknown to me, but it certainly seems plausible. The tomato hornworm moth Manduca sexta certainly has a long enough tongue (proboscis).

6. 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).