Native Hawaiian Garden (7722)

‘Āweoweo or ‘Āheahea (Chenopodium oahuense) – Island Giants

Evolution often behaves in predictable yet poorly understood ways on islands. Such is the case with insular arborescence, a frequent phenomenon on islands where small herbaceous founder species evolve into woody treelike species. ‘Āweoweo, the tallest Chenopodium in the world, is an excellent example of insular arborescence. If you grew up in the continental USA and know your plants, you likely think of Chenopodium, commonly called goosefoots because their leaves resemble the footprint of a goose, as short (less than two feet tall) fleshy often-weedy herbs. This characterization is true for nearly all Chenopodium worldwide. However, here in Hawai‘i, I have seen ‘āweoweo in Kohala (on the Big Island) that were nearly ten feet tall! (Karl Magnacca, an entomologist working for the O‘ahu Army Natural Resources Program, has seen ‘āweoweo even taller – much taller. Check out his photos of Chenopodium oahuense on flickr.com.)

Insular arborescence in Hawai‘i is not limited to ‘āweoweo. Some endemic Hawaiian species of Euphorbia (‘akoko), Nototrichium (kulu‘ī), Charpentiera (pāpala), Viola (pāmakani or ‘olopū), and Scaevola (naupaka) are among the tallest and woodiest in the world. Interestingly, some of these woody native trees and shrubs (i.e., Chenopodium, Nototrichium, and Charpentiera) do not have the wood morphology typical of ordinary trees. Rather, their pseudo-wood is made up of layers of hard and soft tissue somewhat like a rolled-up newspaper. (Hawaiians discovered this unusual wood could be used to make entertaining fireworks.)

Biologists still do not clearly understand why we see insular arborescence. Two hypotheses put forth for Hawaiian species are: (1) There were(are) unoccupied niches for tree species in Hawai‘i's forests because of the difficulty in reaching the Islands. These niches were filled by fortuitous small herbaceous founders that evolved into taller and taller species. (2) Herbaceous founder species from temperate regions that were limited to less than a year's growth, now, in Hawai‘i, with its subtropical climate, had multiple years to grow larger and woodier.

Habitat & Appearance: While ‘āweoweo is endemic to Hawai‘i, it has a very wide range within the Islands. Wild plants have been found on all the main Hawaiian Islands except Kaho‘olawe (although it's very likely it once grew there), as well as many of the Northwestern Hawaiian Islands (i.e., Lisianski, Laysan, French Frigate Shoals, Necker, Nīhoa). Within the last 20 years, ‘āweoweo has been planted out extensively in flora and fauna restoration efforts on islands such as Midway and Kaho‘olawe. Some native birds such as the Nīhoa finch (Telespiza ultima) use ʻāweoweo for food, nesting material, and nesting sites. On the main Hawaiian Islands, ‘āweoweo is common in coastal areas and lowland dry forests and shrublands. Additionally, on Maui and Hawai‘i, it grows in subalpine shrubland.

‘Āweoweo is a polymorphic species varying in stature, scent, and leaf size, margins, color and pubescence. Coastal forms are often short (less than 3 feet) or even prostrate, while montane forms are generally taller or treelike (up to 20 feet). As detailed in the next section, ‘āweoweo leaves, flowers, and fruits can be scentless or have a strong fishy fragrance. Stems sometimes have a pattern of red streaks. All ‘āweoweo leaves tend to have the same goosefoot shape, however, they can vary considerably in size from ½ inch to 2 inches long. This size variation is both genetic, as well as environmental (e.g., plants produce larger leaves during the rainy season and smaller leaves during the dry season). ‘Āweoweo leaves are most commonly fleshy and olive green with tiny hairs that give them a grayish or bluish-silver appearance. However, plants with darker green paper-thin leaves are not rare, particularly in wetter habitats. The tiny flowers of ‘āweoweo are clustered on a panicle. These mature into tan to brown multi-fruited spikes.

Panicles with flowers and ripe utricles (fruits). Seedlings. Prostrate ‘āweoweo with ‘ilima and pā‘ū-o-Hi‘iaka. ‘Āweoweo shrub on Midway Atoll. (Prostrate and Midway shrub photographs courtesy of Forest & Kim Starr CC BY 2.0). Treelike ‘āweoweo in Kohala.

‘Āweoweo in Hawaiian Culture: The two Hawaiian names for this plant, ‘āweoweo and ‘āheahea, are very descriptive. ‘Āheahea means "to wilt," a common response of this plant's leaves to the drought conditions it often experiences. In the Kumulipo, the Hawaiian creation chant, many animals and plants were created in pairs such that when one organism was created in the ocean there was a counterpart created on land. So, while ‘āweoweo is the name of a plant, it is also the name for Hawaiian bigeye (Priacanthus spp.), a genus of all-red reef fish. What makes this shared name particularly appropriate is that the leaves, flowers, and fruits of some ‘āweoweo, when crushed, smell overwhelmingly like a fish. The red streaking sometimes seen on ‘āweoweo stems is also considered by Hawaiians as further evidence of the plant-fish connection. For a long time, I thought all ‘āweoweo (the plant) had this fishy fragrance, until a hiking trip in West Maui with my friend Anna Palomino. Upon encountering an ‘āweoweo growing on a roadside cliff, I shared with Anna the Kumulipo connection. She responded by telling me she had never encountered an ‘āweoweo on Maui that smelt like a fish, and, sure enough, this cliff-face ‘āweoweo was scentless.

Hawaiians would wrap the leaves and shoots of ‘āweoweo in kī (Cordyline terminalis) leaves, cook them in an ʻimu, and eat them when food was scarce. They also used ‘āweoweo wood in composite fish hooks. Medicinally, ‘āweoweo was used to treat children with ‘ea (thrush) and pā‘ao‘ao (ailments), sometimes mixed with other ingredients. The Bishop Museum Ethnobotany Database notes: “The kahuna ho‘omanamana called this plant ‘iloe holokula, because it was used everywhere to induce death…[also used] with the ‘ākia lau nui (Wikstroemia) and some bitter plants as firewood in the fireplaces used to send prayers.〞

Collecting Seeds: ‘Āweoweo flower and fruit almost continuously except during prolonged periods of drought. Even then, you are likely to see old panicles with mature fruits. The tiny fruits of ‘āweoweo are botanically referred to as utricles – small thin-walled one-seeded somewhat inflated fruits. They are clustered on a panicle (a type of inflorescence) that turns from green to tan or brown when the utricles are mature. You can collect the ripe utricles by hand; they easily break off the panicle into your palm if you cup your hand around the panicle and gently pull. Alternatively, you can cut off the panicles, place them in a ziplock bag, and massage the bag until the utricles break off and fall to the bottom of the bag. I normally sow ‘āweoweo utricles shortly after collecting them. However, they can be stored in a refrigerator for, perhaps, as long as 1-2 years. After a year, most of my seeds were nonviable, however, if sown in-mass, you may get some spouts.

Growing from Seed: I have experienced mixed results with ‘āweoweo seed. Most often, I get a high percentage of germination from the freshly-collected utricles I have sown. However, occasionally, very few or even none of the seeds germinate. There may be a couple of reasons for this according to David Duvauchelle at the USDA: (1) Cultivated ‘āweoweo produce seed with very low germination rates, and (2) Because ‘āweoweo often produces seed continuously, the majority of the seed harvested might be immature. Of these two reasons, I am more inclined to believe the first is the more likely reason for my bad luck. However, I have also had bad luck with utricles I have collected from some wild ‘āweoweo, and very good success with utricles I have collected from some cultivated ‘āweoweo. Therefore, I think seed viability may have more to do with an individual ‘āweoweo's ability to successfully pollinate itself (or closely-related nearby ‘āweoweo) and produce viable seed. In other words, perhaps, some, but not all, ‘āweoweo can only produce viable seeds when they are pollinated by a second genetically-different ‘āweoweo. Whatever the reason may be, if you experience poor germination with your ‘āweoweo seed, try collecting again from a different plant or location.

Do not try to separate ‘āweoweo seeds from their thin fruit; you should sow the utricles directly. Methods One, Two, and Three all work for ‘āweoweo, and soaking or not soaking the utricles before sowing does not seem to make a difference. I prefer to use Method Two or Three, sowing a few to several utricles in each container. Later, I cull all but one of the sprouts from the pot. Seeds normally begin sprouting in 1-2 weeks and continue for another month. It takes 1-2 months for the seedlings to develop four true leaves; if you are using Method One, this is the best time to transfer the seedlings to individual containers. Seedlings grow quickly, particularly if you give them good light (i.e., 50% to 100% full sun) and a little fertilizer, and should be 8-12 inches tall in about three months. Once they reach this size, plant them out in your garden or restoration site. If you have grown your ‘āweoweo seedlings in less than 50% sun, acclimate them to the light level in your garden with a temporary sun-shield – be creative!

Growing from Cuttings: It is possible and sometimes preferable to grow ‘āweoweo from cuttings such as when you want to retain a particular variety (e.g., prostrate ‘āweoweo). Using Method One or Two, ‘āweoweo cuttings root in about two months. I have limited experience rooting ‘āweoweo. However, the few I have grown from cuttings seemed less vigorous and had a shorter lifespan than those grown from seed.

Growth in the Garden: My experiences with ‘āweoweo are limited to the prostrate and erect shrub forms; I have never grown any of the treelike forms. ʻĀweoweo will grow in partial shade but does best in full sun. Water your new planting until it is well established (2-3 months) in the site. After that, water only during prolonged drought. In fact, watering too often can cause root-rot and kill your ‘āweoweo. ʻĀweoweo is not fussy about soil type, growing well in sand, clay, and rocky soils. Likewise, ‘āweoweo in the ground do not need fertilizer. In about a year or less, your plant should be 2-4 feet tall (or wide if prostrate) and flowering and fruiting. Occasionally, one or more main branches will die for no apparent reason. Most of the erect shrub forms of ‘āweoweo I have grown (O‘ahu strains) have died after about five years, seemingly from senescence. If this is generally true of ‘āweoweo, you should plan on periodic replacements for your garden. (I suspect treelike ‘āweoweo live much longer than five years.)

Diseases & Pests: I have never had much of a problem with pests or diseases attacking ‘āweoweo. Occasionally, a small gray weevil (Myllocerus sp.) will eat the leaves, or aphids or mealybugs will infest the stem-tips; ants often protect and spread these two sap-sucking pests. Refer to Enemies in the Garden for methods of combating these pests. In the field, Forest & Kim Starr have seen leaf damage by the Hawaiian beet webworm (Spolodea recurvalis).

Ā ā Ē ē Ī ī Ō ō Ū ū