Boerhavia repens
Nyctaginaceae or Four-o'clock family
Synonyms: Boerhavia diffusa, Boerhavia diffusa var. gymnocarpa, Boerhavia diffusa var. pseudotetrandra, Boerhavia diffusa var. pubescens, Boerhavia diffusa var. sandwicensis, Boerhavia mutabilis, Boerhavia tetrandra
Alena
Anena (Niʻihau), Nena
Red spiderling
Natural Range & Environment
Boerhavia repens is native to much of Africa, Asia (e.g., India, China, Japan, and New Guinea), Australia, and islands in the Pacific Ocean including Hawai‘i. It has also been introduced to Spain and Easter Island [World Flora Online].
In Hawai‘i, alena has been found on most of the Northwestern Hawaiian Islands (i.e., Kure, Midway, Pearl & Hermes, Lisianski, Laysan, French Frigate Shoals, Nīhoa) as well as all the main Hawaiian Islands [Flora of the Hawaiian Islands]. It grows in coastal, usually dry, areas [Wagner et al. 1990] in both sandy and rocky sites.
Alena produces clusters of tiny pink to white flowers positioned atop a long stalk. When pollinated, the flowers develop into tiny semi-sticky fruits. (Closeup photographs of flowers and fruits courtesy of Joel Lau ©.) Alena has a large tuberous root (Photograph courtesy of Forest & Kim Starr CC BY 3.0 US.). Wild alena grow in both sandy and rocky coastal areas (Photograph of alena in sand courtesy of Joel Lau ©; photograph of alena on large rock courtesy of Forest & Kim Starr CC BY 3.0 US.).
Description
Boerhavia repens is a short-lived (less than five years) perennial herb with a large tuberous root and few to several prostrate stems radiating from its root crown. Its light green egg-shaped leaves can be up to two inches (5 cm) long and are sometimes slightly crinkled. The leaf surfaces can be slightly pubescent to hairless.
Alena produces clusters of tiny pink to white perfect (bisexual) flowers positioned atop a long stalk. When pollinated, the flowers develop into small ovoid 5-ribbed single-seeded sticky fruits that easily detach from their stalk when ripe. The sticky fruits undoubtedly help with seed dispersal by animals, primarily birds, and are very likely the reason for the species' wide geographic distribution. However, it should be noted that the fruits of Boerhavia repens, at least in Hawai‘i, are not nearly as sticky (or annoying) as the fruits of the introduced and naturalized B. coccinea (Scarlet spiderling).
Growth Requirements
General
Sadly, I (Koebele) don’t know anyone who actually grows alena on purpose. Rather, it just tends to pop up in coastal restoration sites. Perhaps this is because people mistake it for the introduced (and naturalized) weed Boerhavia coccinea (Scarlet spiderling) which has super-sticky fruits that annoyingly get tangled in shoes, socks, and other clothing. While alena does have semi-sticky fruits, I cannot remember spending any time removing them from my clothing. Therefore, hopefully, you will give this butterfly-attracting coastal plant a try in your landscape.
Alena does best in a site with full sunlight for all or most of the day. While it will grow in shaded places, expect to see fewer flowers on these shaded plants.
Wild alena grow in dry places in well-drained soil (i.e., sandy or rocky sites). Therefore, once established in your landscape (in about a month), avoid overwatering your alena; in fact, you probably will not need to water it at all!
Alena can tolerate extreme heat, drought, strong winds, and salt spray. It will grow in just about any soil (or media) type, provided the soil drains water quickly. However, it seems to grow and replace itself with new seedlings best in sandy or rocky soil (or media).
Alena grows and matures quickly, and you can expect to have a flowering plant one to two feet (30 to 61 cm) in diameter (if branching) or long (if non-branching) in about six months. If your alena doesn't naturally branch, try repeatedly cutting off the growing stem tips to encourage branching and a fuller appearance. In-the-ground alena do not require any fertilizer. However, if kept in a container, you may want to apply a single-digit balanced controlled-release fertilizer every 6 to 12 months, or feed your alena with a foliar fertilizer at ⅓ to ½ the recommended strength every couple of months.
Unfortunately, alena are short-lived, and you should not be surprised if your plant dies after a couple of years. However, if you have planted your alena in a sandy or rock site, it's likely you'll see its progeny (i.e., seedlings) surrounding it before it dies. If you don't see these seedlings after a year or so, collect, air dry, and store some of your plant's many ripe fruits in your refrigerator. The single-seeded fruits are relatively easy to sprout in clean sand. Alternatively, you can extend the life of your alena by rooting stem cuttings in perlite using a rooting hormone; however, this is a bit more difficult.
Pests and Diseases
Cultivated alena are infrequently infested with sap-sucking insects like aphids, mealybugs, and scale insects. Also, be on the lookout for snails and slugs that may chew on your plants. Refer to the Pests & Diseases page for treatments to control these pests. While we have not seen larvae of the white-lined sphinx moth (Hyles lineata) on any of our plants, Forest and Kim Starr have seen this alien insect consuming the leaves of wild alena. These can be easily removed from the plant by hand.
White-lined sphinx moth larva (Hyles lineata) on alena (Photograph courtesy of Forest & Kim Starr CC BY 3.0 US.).
Adult white-lined sphinx moth (Hyles lineata) (Photograph courtesy of Greglinscott CC BY-SA 4.0.).
Uses
Ancient Hawaiian
Hawaiians used alena's tuberous roots medicinally [Neal 1965], possibly as a diuretic [Pukui & Elbert 1986].
Modern
Today, alena is still used medicinally by local herbalists for a variety of illnesses [Leonard 2012]. Outside Hawai‘i, Boerhavia repens is both eaten and used medicinally as a diuretic as well as to treat several illnesses [Useful Tropical Plants].
Special Features and Information
General
Nyctaginaceae is a small family of about 290 species in 33 genera, primarily found in tropical and subtropical regions of the world [WikipediA;Nyctaginaceae]. In Hawai‘i, common non-native members of the family include several Bougainvillea species and hybrids, as well as the garden four-o'clock (Mirabilis jalapa), locally called pua ahiahi, which translates as the "late afternoon (becoming evening) flower" [Pukui & Elbert 1986].
In addition to Boerhavia repens, there are two other native Boerhavia species in Hawai‘i, the indigenous B. acutifolia and the endemic B. herbstii. Other Nyctaginaceae native to Hawai‘i include five species of pāpala kēpau (two indigenous and one endemic species of Ceodes, the indigenous Pisonia grandis, and the endemic Rockia sandwicensis) [Flora of the Hawaiian Islands].
Hawaiian Name
Anena is the name for this species on Niʻihau. Boerhavia repens shares the Hawaiian name, nena, with Heliotropium curassavicum, an indigenous coastal herb, also called kīpūkai [Pukui & Elbert 1986].
Etymology
The genus Boerhavia was named by Linnaeus to honor his friend, Hermann Boerhaave (1668–1738), a botany professor at the University of Leiden [Wagner et al. 1990]. The species name, repens, can mean "creeping" or "prostrate and rooting," likely referring to the species' habit of growing along the ground [A Grammatical Dictionary of Botanical Latin].
BPK