Natural Range & Environment

    Delissea rhytidosperma is endemic to Kauai in mesic forests from 260-915 m (c. 853-3001 ft). It is known historically from a number of scattered locations east of Wainiha Pali and Nonopahu Ridge; however, all but one of these populations have been destroyed. In 1994, the single surviving population consisted of a dozen individuals, but by 2001, it had declined to just nine individuals [Lammers 2005]. 

Description

    Delissea rhytidosperma is a branching shrub growing up to 2.5 m (c. 8 ft). The leaves, having toothed margins, are alternately arranged, lance-shaped or elliptic, are 8–19 cm (3.25 to 7.5 in) long, and 2–5.5 cm (c. .75 to 2 in) wide with toothed margins. The leaf blade is widest at or above its middle (toward the tip). Leaves often continue on the mid to upper parts of the branches.

    The greenish-white tubular flowers (14–20 mm long), often with violet tinges, are arranged in clusters of 5 to 12. The flowering period for Delissea rhytidosperma is from mid-June to late December, with fruiting from early July to January [Lammers 2005]. (Under cultivation, plants are sporadic but reliable bloomers year-round). The nearly spherical dark purple berries (fruits) contain numerous small white seeds.

Key Differences Between the Kauaʻi Delissea species

Growth Requirements

General

    Delissea rhytidosperma is one of the easiest and most rewarding plants in the Lobelia family to grow and maintain in a landscape. Delissea can be grown as understory plants under trees protected by shrubs and ferns. Though not lowland plants, they do well at near sea level in pots or in the landscape, provided they have good drainage. In general, Delissea sp. require vigilant monitoring for pests, diseases, or other problems. Watch for spider mites in the hotter months; snails and slugs in the rainy months. Spider mites may infest and destroy all of the plant's leaves and weaken the plant, which invites other opportunist pests such as scale, mealybugs and aphids to take hold and intensify the damage. At least as a temporary, and sometimes permanent fix, spray mist the undersides of the leaves for spider mites. But plants will likely need some sort of miticidal spray or systemic for best control. If not treated, these pests may even eventually kill the entire plant. However, even if you lose all the leaves due to spider mites, do not give up on this or any other Hawaiian lobelioid, nor toss it out prematurely. The reason is that the Hawaiian Campanulaceae (Bellflower family) have an amazing resilience to bounce back and once again leaf out, flower and produce fruit! I (Eickhoff) have seen seemingly hopeless plants coming "back to life" with a little patience and extra TLC.

    Despite these seeming challenges, we still encourage you to grow one or more of these beautiful plants once you feel you have the experience and dedication to "put in the work." This large group of Hawaiian bellflowers is found nowhere else in the world, and, without exception, all of them are incredibly beautiful, with some being truly spectacular!

    Given the above caution, Delissea rhytidosperma is still one of the easiest of the Hawaiian lobelioids to grow and maintain. Use it as an accent planting or in clusters in semi-shady locations. It does well at low elevations in the ground or in a container, provided the site or pot has good drainage. ʻOha grows best in partially sunlit sites and organic or cinder-rich soils or media. Keep the soil or media anywhere from moist to moderately wet. ʻOha is intolerant of salt spray, and its stems can snap in strong winds. While it is okay to remove dead leaves, spent flowers, or fruit, avoid pruning any of its stems.

    Though I (Eickhoff) have had excellent success with growing it outdoors, ʻoha may be grown indoors, "and one can argue, maybe easier to keep inside than outside" (Koebele). Place ʻoha near a window to provide it with bright but filtered light or full-morning sun, or keep it under full-spectrum lamps (LEDs work well). Keep the potting media moist, and drench fertilize (with a standard organic or inorganic fertilizer) once a month or apply a slow-release balanced fertilizer every six months. Though the plant will escape most pests indoors, keep a close lookout for spider mites.

Pests and Diseases

    Outside, Delissea rhytidosperma is attacked by spider mites, aphids, mealybugs, ants, slugs, snails, mice, and rats. Snails, slugs, mice, and rats are the most deadly pests because they can girdle or severely damage the basal stem of the plant and kill it (sometimes in a single night!). Inside, spider mites are generally the pest to worry about most because they will distort the leaves or make them look spotty and/or crinkly. Ultimately, the leaf dies, and any new leaves the plant tries to produce are also attacked. Refer to the Pests & Diseases page for ways to battle these pests.

Special Features and Information

General

    The Bellflower family (Campanulaceae) is a large family of mostly herbaceous plants with about 2,400 species within 84 genera with a worldwide distribution and a wide diversity of habitats. Plants often have a milky sap [WikipediA; Campanulaceae].

    There are over 100 endemic Hawaiian species of Campanulaceae. Delissea is an endemic Hawaiian genus with about 15 species; there is still some taxonomic debate on the exact number. Until recently, Delissea kauaiensis was informally lumped in with Delissea rhytidosperma [Lammers 2005]. The overwhelming number of Delissea species are extinct, with the remaining handful either extinct in the wild or critically endangered. In the past, the genus Cyanea was placed in Delissea [Flora of the Hawaiian Islands]. The video Kauaʻi conundrums: Dubious Delissea – untangling the taxonomy of the Hāʻupu population explores the potential hybridization between Delissea kauaiensis and D. rhytidosperma at Hāʻupu, focusing on the unique plants exhibiting characteristics of both species in this area. (Note that this video begins at the point where it addresses the Hāʻupu population. For an overview of the genus Delissea and particularly featuring the two Kauaʻi species, start at the beginning).

Hawaiian Name

    Though Hawaiian Plant Life--Vegetation and Flora [Gustafson et. al 2014] uses the name ʻOha for the four Delissea spp. featured in their publication, it may appear to be a recently-adopted Hawaiian name. That said, ʻOha is the name we will use within this website.

Etymology

    The genus Delissea is named after Jacques Delisse (1773–1856), a Frenchman who joined the Baudin expedition to Australia that sailed from Le Havre in October 1800, as a botanist-pharmacologist. Suffering from scurvy, he left the ship when it reached Mauritius the next year and set up as a pharmacist in Port Louis [WikipediA; Jacques Delisse]. The specific epithet is from the Greek rhytidos, wrinkled, and sperma, seed, in reference to the wrinkled seeds of this species. However, this wrinkled appearance, looking much like a brain, is also seen in at least two other Delissea spp. [Gledhill 2008; Lammers 2005].