‘Uhaloa (Waltheria indica) – Speaking a different language.
Recently (Fall 2022), I was helping Professor Daniela Dutra Elliott's Botany students with a native Hawaiian plant propagation activity. A few months earlier, I had come across an online paper by Scott B. Lukas, Joseph DeFrank, and Orville C. Baldos (in HortScience, Volume 51: Issue 9, 2016) detailing their experiments to discover an effective method of propagating ‘uhaloa from seeds. Daniela and I wanted her students to duplicate (and, hopefully, verify) a very successful technique Lukas et al. had discovered. However, rather than just telling the students what to do, we decided it would be more educational if the students read the paper (via their cellphone) and told us how they would duplicate the experiment.
Part of my graduate education was learning how to critically read (and write) a scientific paper. Today, I take that skill for granted. In contrast, Daniela's students found the HortScience paper a bit overwhelming – until I told them to focus on the Abstract (i.e., summary) at the top of the paper. After that, they did remarkably well at telling us what the paper described and how they could replicate the effective seed technique. (See a photograph of their amazingly successful mini-experiment below.)
This experience made me wonder how we can better translate the language of the professional horticulturist into something non-scientists can understand and benefit from. Requiring everyone to go to graduate school is clearly not the answer. However, I hope any professionals reading this webpage will take my concern to heart, and try in the future to share their amazing discoveries not only with their colleagues, but, in a more welcoming language and format, with the many amateur horticulturists out there.
Habitat & Appearance: A pantropical short-lived subshrub or shrub with velvety rugose oblong to oval leaves with toothed edges. Tiny fragrant yellow flowers are tightly clustered in its leaf axils, with each flower maturing into a tan to brown dry capsule containing a single black seed. ‘Uhaloa is indigenous to Midway and all the main Hawaiian Islands where it grows in dry and disturbed areas.
I have seen two forms of ‘uhaloa, a prostrate coastal form, and an upright form more common at inland sites. To date, I do not know if this difference is genetically based, as is the case with ‘ilima, or purely an environmental response.
(Top to Bottom) Mature plant with flowers. (Left to Right) Embryo, scarred seed, unscarred seed. Seedling. Dramatic results of students' scarification experiment. (Header photograph courtesy of Forest & Kim Starr ©.)
‘Uhaloa in Hawaiian Culture: The flowers, leaves, and roots of ‘uhaloa were (and are) used by Hawaiians for numerous illnesses including bronchial infections, asthma, and as a pain reliever, primarily to soothe a sore throat. Leaves were pounded and used to fill in cracks on canoes. In the past, ‘uhaloa was often classified as a weed in farmland, pastures, and along roadsides.
Collecting Seeds: ‘Uhaloa produces flowers and fruits throughout most of the year, only taking a break during periods of extreme drought. Collect the browning fruit clusters by hand. (A later study by Lukas et al. (2019) discovered that the maximum seed yield came from clusters that were slightly older (i.e., more brown fruits) than those in the header photograph above.) Back at home, let the clusters dry out for several days in an open bowl or similar container. Then, rub the clusters between your fingers to break open the fruit capsules and release the tiny black seeds. Test the seeds for viability in a cup of water; the viable seeds will sink. (These are tiny seeds that can be buoyed up by surface tension. Therefore, stir the water or use your finger to submerge each seed to confirm its viability.) I have never stored ‘uhaloa seeds for more than a few months. However, Lucas et al. in their 2016 study found “Nonscarified seeds exhibited minimal loss of viability during 10 months of storage at 5 °C at 12% and 50% relative humidity (RH), but a significant decline in viability of scarified seeds was detected."
Growing from Seed: The germination hack that Lucas et al. (2016) discovered for ‘uhaloa was mechanical scarification. They scarred the seeds using two methods not really practical for the average native Hawaiian plant enthusiast, using a scalpel under a microscope and using a mechanical electric drum scarifier lined with 80-grit sandpaper. Therefore, I modified their method by using two small squares of 180-grit sandpaper. (I encourage you to experiment, and discover an even better at-home scarring method.) I placed one sandpaper square on a hard flat surface (e.g., table), placed one seed on the square, and then covered the seed with the second sandpaper square. Pressing down gently on the top square and moving my hand in a circular motion for about 30 seconds, I was able to scar the seed between the two pieces of sandpaper. I repeated this procedure for each seed I intended to sow. Occasionally, I would apply too much pressure and crush the seed. Also, sometimes my technique would crack the seedcoat, leaving an uninjured embryo. The photograph to the right shows an uninjured embryo, a scarred seed, and a non-scarred seed. (Note that the scarred seed does not look much different from the non-scarred seed, perhaps the only visual clue being the seedcoat dust covering and surrounding the seed.)
Sow 2-3 scarred seeds or uninjured embryos in a pot using Method Three. Or, as in Daniela's students' experiment, sow several scarred seeds and embryos in a community pot; you will later need to separate and repot the individual seedlings. In 2-3 weeks nearly all of the seeds will have sprouted. (To date, I have not determined if uninjured embryos germinate the same, better, or worse than scarred seeds.)
In the nursery, ‘uhaloa seedlings grow best in 50%-0% shade, with or without fertilizer, and should be 6-12 inches tall in 3-6 months; plant them into your garden at this size. Seedlings are occasionally infested by sap-sucking insects such as aphids and mealybugs. Refer to Enemies in the Garden for methods to combat these pests.
Growing from Cuttings: I have tried a few times to root ‘uhaloa cuttings with very limited success. The few resulting plants were always less vigorous than seedlings. I have also successfully potted up tiny seedlings I find in the garden or field. These should be kept in a shaded sealed clear container or a mist chamber for several days until their roots recover.
Growth in the Garden: Plant your ‘uhaloa in the sunniest and driest spot in your garden, water it weekly for a month, and then ignore it. It should grow to maturity (i.e., flowering) in 3-6 months with little or no care. The most common mistake people make with ‘uhaloa is overwatering which can kill it. Just remember that ‘uhaloa naturally grows in very dry locations which you should try to mimic. Unfortunately, even well cared for ‘uhaloa do not seem to have a very long lifespan — normally five years or less. However, it is not uncommon for seedlings to sprout directly beneath a mature plant. You can take advantage of this by pruning the adult plant down to its base when it dies, and letting one of its seedlings grow as a replacement. Collecting and storing seeds in your refrigerator is also good insurance.
Diseases & Pests: I have never had to deal with any diseases or pests of consequence for ‘uhaloa. Any problems you might have are more likely the result of overwatering or over-shading your plant. Forest & KIm Starr have numerous photo-records of Eublemma accedens, a small moth, and its larvae which feed on ‘uhaloa.
Ā ā Ē ē Ī ī Ō ō Ū ū