Differs from Hawai‘i congeners by its combination of opposite, long, elliptic to narrowly elliptic or ovate-elliptic leaves with revolute margins; caducous stipules 7–10 mm long, externally glabrous with dense hirtellous-pilose hairs near the margins of the inner surface; unbranched inflorescences with peduncles 20–28 mm long; flowers 6–8 per cluster; and persistent calyx tube with 4–8 irregular dentate lobes.

USA. Hawai‘i. Kaua‘i: Lihu‘e District, ridge below Kawaikini, Ioli headwaters, 26 Aug 1999, K.R. Wood & M. Query 7978, (holotype: PTBG-050238; isotypes (to be distributed): BISH, MO, P, US, WU).

Trees 2–4 m tall, dioecious, bark grey-brown, trunk with branches or knobby protuberances; branchlets glabrous, light brown, 3–4 mm diam., nodose with leaf and stipule scars. Leaves opposite, decussate, glabrous, blades elliptic to narrowly elliptic or ovate-elliptic, 40–76 ×11–22(–26) mm, pinnately veined with 8–10 pairs of secondary veins, higher level venation conspicuously reticulate, occasionally impressed adaxially, small pit domatia often present located abaxially along midrib near juncture with secondary veins, sometimes absent, margins slightly revolute, apex acute, base attenuate and decurrent; petioles 5–11 mm long, narrowly winged distally, purple-brown; stipules 7–10 mm long, connate for 1/3–1/2 of their length into a cylindrical sheath (1–)2–4 mm long, free apical portion (3–)4–6 mm long, acuminate to a conspicuous, thickly carinate-subulate apex with a claw-like appendage, externally glabrous, internally densely hirtellous-pilose distally, sheath margins with shortly ciliate fringe and sometimes a few short callous protuberances or glandular appendages 0.1–0.2 mm long, as long as the ciliate hairs. Inflorescences axillary, mostly simple and capituliform, subtended by a pair of connate, broadly ovate bracts, 6–8-flowered, peduncles 20–35 mm long, or rarely bearing an additional peduncle with one additional pair of subsessile, 3–5-flowered cymules subtended by connate, broadly ovate bracts 2–3 × 2–3 mm with ciliate margins. Flowers: staminate flowers mostly in groups of 6–8 on peduncles 20–28 × 0.7–0.8 mm, subtended by a pair of connate, broadly ovate bracts 2–3 × 2–3 mm with ciliate margins; flowers subsessile, the calyx cup-shaped, irregularly (4–)8-lobed, cup 0.8–1 mm long, the lobes 1–2.2 × 0.8–1.5 mm, apex entire or irregularly 2–4-dentate, glabrous or sparsely hirtellous; corolla (only seen in bud) glabrous, 6–6.5 mm long, the tube 2–3 mm long, 4–5-lobed, the lobes 3.5–4 mm long, stamens 8, the staminal filaments 1.5–2 mm long, the anthers 3.6–4 mm long, apex acuminate, base sagittate, the pistillode 2.5 mm long. Female flowers and inflorescence not seen. Infructescences with peduncle 20–28 mm long, flattened, fruits in terminal cluster of 3–6 subtended by cupuliform pair of connate bracts 2–3 × 2–2.5 mm, margins ciliolate; fruits orange when fresh, broadly ellipsoid to broadly obovoid, 5.5–6 × 4.5–5 mm, glabrous, surface drying wrinkled, weakly 4-ribbed, apex with persistent irregularly lobed calyx 1.5 mm long. Pyrenes 2, broadly ellipsoid to broadly obovoid, plano-convex, 5.7–6 × 4.1–4.5 mm, brown, with low dorsal ridge in distal 1/3–1/2.

Figure 1. 

Coprosma kawaikiniensis K.R.Wood, Lorence & Kiehn, sp. nov. (holotype: PTBG).

To date, Coprosma kawaikiniensis has been observed in flower during early April, and with fruit from late August to mid-September.

The new species is named after the holotype locale, Kawaikini, the highest peak on Kaua‘i and one of the rainiest places on earth (Juvik and Juvik 1999). Literally, Kawaikini means “the multitudinous waters” in Hawaiian (Pukui et al. 1974).

The volcanic island of Kaua‘i is the oldest of the main high Hawaiian Islands (ca. 5 Ma) featuring a physical geography that is quite variable with deeply eroded drainages, well-defined canyons, and tall coastal seacliffs. It is also the most floristically rich Hawaiian Island (Wagner et al. 1990, Imada 2012) exemplified by high levels of habitat diversity and endemism, which includes ca. 244 single island vascular plant endemics (Wood 2015). Careful botanical research conducted over the last few decades by staff of the National Tropical Botanical Garden (NTBG), especially around cliffs and remote regions, has contributed 32 new published plant taxa from Kaua‘i (Imada 2012).

The recent discovery of Coprosma kawaikiniensis was made around extremely steep, narrow wind swept ridges, slopes, and boulder strewn stream banks below Kawaikini, the highest peak on Kaua‘i which summits at 1598 m elevation (Figures 2–4). This particular habitat is the remotest of Kaua‘i’s eco-regions and can be further characterized by its mist-shrouded, dark, narrow basalt canyon walls seeping with springs, and having the distinction of being one of the rainiest places in the world (Juvik and Juvik 1998). The holotype region represents a previously undescribed plant community dominated by two Hawaiian endemic genera, namely Dubautia Gaudich. (Asteraceae) and Sadleria Kaulf. (Blechnaceae), referred to as the Dubautia-Sadleria shrubland-fernland (DSSF) community (Wood 2013; Figures 2, 3). To date, fewer than 50 individuals of C. kawaikiniensis have been documented, occurring in elevations between 1035 to 1350 m.

Figure 2. 

Landscape habitat where Coprosma kawaikiniensis was discovered below Kawaikini, Kaua‘i, showing rugged terrain and the Dubautia-Sadleria shrubland-fernland (DSSF) community.

Figure 3. 

The Dubautia-Sadleria shrubland-fernland (DSSF) community below Kawaikini, Kaua‘i.

Figure 4. 

Map showing location of Coprosma kawaikiniensis near Kawaikini summit, Kaua‘i, Hawai‘i.

The DSSF community is predominantly low-statured at 1–2(–4) m tall and is composed of several species of Dubautia including Dubautia imbricata H.St.John subsp. acronaea G.D.Carr, D. knudsenii Hillebr. subsp. nagatae (H.St.John) G.D.Carr, D. laxa Hook. & Arn. subsp. hirsuta (Hillebr.) G.D.Carr, D. paleata A.Gray, D. raillardioides Hillebr., and on rare occasions D. pauciflorula H.St.John & G.D.Carr. The four species of Sadleria that also dominate this community are Sadleria cyatheoidesKaulf., S. pallida Hook. & Arn., S. souleyetiana (Gaudich.) T.Moore, and occasionally S. squarrosa (Gaudich.) T.Moore.

Some of the more common herbs, shrubs and trees, the latter depauperate in physical stature, of the DSSF community include Antidesma platyphyllum H.Mann var. hillebrandii Pax & Hoffm., Astelia argyrocoma A.Heller ex Skottsb., Bidens forbesii Sherff, Broussaisia arguta Gaudich., Coprosma kauensis (A.Gray) A.Heller, Ilex anomala Hook. & Arn., Pritchardia hardyi Rock, Syzygium sandwicensis (A.Gray) Nied., along with several to numerous species of Cheirodendron Nutt. ex Seem., Cyanea Gaudich., Cyrtandra J.R.Forst. & G.Forst., Labordia Gaudich., Kadua Cham. & Schltdl., Lobelia L., Melicope J.R.Forst. & G.Forst., Metrosideros Banks ex Gaertn., Myrsine L., Peperomia Ruiz & Pav., Pipturus Wedd., Platydesma H.Mann, Polyscias J.R.Forst. & G.Forst., Psychotria L., Scaevola L., and Vaccinium L.

Common sedges and grasses of the DSSF are Cyperus sandwicensis Kükenth., Eragrostis grandis Hillebr., Gahnia vitiensis Rendle subsp. kauaiensis (Benl) T.Koyama, Machaerina angustifolia T.Koyama, Panicum lineale H.St.John, along with several species of Dichanthelium (Hitchc. & Chase) Gould.

Besides the dominant Sadleria, there are a number of other common associated ferns found in the DSSF such as Cibotium glaucum (Sm.) Hook. & Arn., Dicranopteris linearis (Burm.f.) Underw., Diplopterygium pinnatum (Kunze) Nakai, Sphenomeris chinensis (L.) Maxon ex Kramer, as well as several species of Adenophorus Gaudich., Asplenium L., Dryopteris Adans., Elaphoglossum Schott, and Hymenophyllum Sm.

Plant communities of the nearby surrounding region are all montane windward wet habitat associations. Open bogs occur in scattered locations along the main upper headwater ridge line and are dominated by genera such as Metrosideros, Rhynchospora Willd., Dichanthelium, Gahnia J.R.Forst. & G.Forst., Machaerina Vahl, Plantago L., Viola L., and Oreobolus R.Br. Several very rare species associated with bogs and bog margins were also discovered, namely Keysseria helenae (C.N.Forbes & Lydgate) Cabrera and Lysimachia venosa (Wawra) H.St.John, a member of the Primulaceae family undocumented since 1911 (Wood 2013). Occasional stands of Metrosideros-Cheirodendron forest with low-statured canopies of 5–7 m also occur in a mosaic of random patches surrounding the DSSF community, and Coprosma kawaikiniensis has also been observed ranging into this habitat. These forests are usually dominated by a significant diversity of mixed understory associates very similar to that of the DSSF. The riparian regions that dissect these relic Metrosideros-Cheirodendron forests and form the headwater drainages that feed the respective lower elevation valleys retain a flourishing treasure trove of rare plant taxa along nearby stream banks, including endangered species of Cyanea, Cyrtandra, Hesperomannia A.Gray, Isodendrion A.Gray, Labordia, Melicope, Phyllostegia Benth., Platydesma, and Polyscias.

Vegetation cover on several nearby steep slopes is composed of just a few species of matting ferns (i.e., Dicranopteris linearis, Diplopterygium pinnatum, and Sticherus owhyhensis (Hook.) Ching) and may be the resulting succession of past landslides. Vertical wet cliff communities of sedges, herbs, and ferns, accentuated with numerous waterfalls form the prevalent back-drop that tower over and surround these habitats below Kawaikini (Wood 2014) (Figure 2).

The holotype region of Coprosma kawaikiniensis has very few non-native plants and animals, however, C. kawaikiniensis is susceptible to catastrophic extinction through environmental events such as hurricanes, landslides, and flash floods in addition to the incursion of threats from nearby regions. Native habitats in the adjacent lower elevation regions, especially below 730 m, are intensely threatened by habitat degradation from feral goats (Capra hircus L.) and pigs (Sus scrofa L.), predation of seeds by rats (Rattus rattus L. and R. exulans Peale), and competition with non-native plant taxa, especially Axonopus fissifolius (Raddi) Kuhlm., Blechnum appendiculatum Willd., Buddleia asiatica Lour., Clidemia hirta (L.) D.Don, Cyperus meyenianus Kunth, Erigeron karvinskianus DC., Juncus planifolius R.Br., Melastoma septemnervium Lour., Paspalum conjugatum P.J.Bergius, Psidium cattleianum Sabine, Rhodomyrtus tomentosa (Aiton) Hassk., Rubus rosifolius Sm., Sacciolepis indica (L.) Chase, and Sphaeropteris cooperi (Hook. ex R.Muell.) R.M.Tryon. These highly invasive weeds possess the ability to spread rapidly (Smith 1995) and have begun to ingress into the upper watershed habitats of C. kawaikiniensis (Wood 2014).

IUCN Red List Category. When evaluated using the World Conservation Union (IUCN) criteria for endangerment (IUCN 2001), Coprosma kawaikiniensis falls into the Critically Endangered (CR) category, which designates this species as facing a very high risk of extinction in the wild. Our formal evaluation can be summarized by the following IUCN hierarchical alphanumeric numbering system of criteria and subcriteria: CR B1ab(i,ii,iii,v)+2ab(i,ii,iii,v); C2a(ii); D; which reflects a severely limited Extent of Occurrence (EOO) and Area of Occupancy (AOO) of less than 3 km² and a population of less than 50 individuals.

All species of Coprosma from Kaua‘i have stipules shorter than 4.5 mm except for C. kawaikiniensis and C. kauensis. The features distinguishing those two species are the number of the flowers per partial inflorescence [6–8, sometimes with an additional pair of 3–5 flowered cymules in C. kawaikiniensis vs. 3(–5) flowered in C. kauensis], the length of the calyx in staminate flowers (1.8–3.2 mm in C. kawaikiniensis vs. 0.4–0.6 mm in C. kauensis), the length of the staminate peduncle (20–28 mm in C. kawaikiniensis vs. 4–8 mm in C. kauensis), the pubescence of the stipules (externally glabrous in C. kawaikiniensis vs. densely strigose on both surfaces in C. kauensis), and the number and form of the stipular appendage(s) [only 1 terminal claw-like appendage and occasionally a few short, rounded appendages or callous protuberances 0.1–0.2 mm long c. equaling the ciliate marginal hairs in C. kawaikiniensis, vs. (3–)5–7(–8) pairs of thickly ovoid to digitate, shiny dark brown-black marginal appendages 0.3–0.5 mm long in C. kauensis] (Figure 5).

Figure 5. 

Stipules and petiole bases of Coprosma kawaikiniensis (AWood 3539, paratype PTBG) and C. kauensis (BPerlman 18645, PTBG). Scale bars in mm.

Species of Coprosma that have stipules of 4.5 mm or greater from the remaining Hawaiian Islands include: C. longifolia A.Gray, C. ternata W.R.B.Oliv., C. rhynchocarpa A. Gray, C. montana Hillebr., and C. ochracea W.R.B.Oliv. Coprosma kawaikiniensis differs from C. longifolia and C. ternata in having opposite vs. usually ternate leaves (with only occasionally opposite leaves on some stems). Coprosma kawaikiniensis has peduncles 20–28 mm long vs. 2.5–16 mm long in C. rhynchocarpa and only 0–1(–4) mm long in C. ochracea. The new species differs from C. montana in having 6–8 flowers per cluster, sometimes with an additional pair of 3–5 flower cymules vs. 1–2 per cluster. In terms of morphology, C. kawaikiniensis most closely resembles C. longifolia (Oahu), but differs from the latter in having opposite vs. usually ternate leaves, stipules with a shorter sheath (1–)2–4 mm long, and free apical portion (3–)4–6 mm long terminated by a thickly carinate-subulate apex with a claw-like appendage, vs. sheath 7–9 mm long and free apical part 2–3 mm long with short-attenuate, acute tip.

The following couplets can be inserted into the existing key to Hawaiian Coprosma by Wagner et al. (1990: 1123) to accommodate C. kawaikiniensis.

(paratypes). United States of America. Hawai‘i. Kaua‘i: Lihu‘e District, ridge running south of Kawaikini, above Iliiliula and Ioli drainage, 1035 m elev., 19 Sep 1994, K.R. Wood, P. Wood, S. Perlman 3539, (BISH, PTBG, US); ridge just south below Kawaikini, 1130-1350 m elev., 03 Apr 2013, K.R. Wood 15460 (BISH, PTBG, US); loc. cit., 03 Apr 2013, K.R. Wood 15463 (PTBG, US, WU).