Peperomia kauaiana K. R. Wood & W. L. Wagner 2026, sp. nov.

Peperomia kauaiana K. R. Wood & W. L. Wagner sp. nov. Figs 1, 2, 3 A – C, 4 Diagnosis. Peperomia kauaiana is morphologically most similar to P. degeneri Yunck. from which it differs by the following combination of characteristics: stem internodes 3–5 mm long (vs. 10–15 mm long), leaves 5 - to 7 - nerved, ovate to ovate-orbicular, 0.5–1.4 (– 1.8) cm long, margins revolute (vs. leaves 3 - nerved, elliptic to oblong-elliptic, 1.5–2 (– 3.5) cm long, margins flat), petioles 0.2–0.5 cm long (vs. petioles 0.8–1.2 cm long) and spikes 1.1–1.7 (– 2.2) cm long (vs. spikes 2.5–4.8 cm long). Type. USA. Hawaiian Islands, Kaua‘i: • Līhu‘e District, Wai‘ahi, 22.014, - 159.501, 830 m alt., 4 Apr 2019 (fl. & fr.), Wood, Perlman & Query 18149 (holotype: PTBG 1000067990!; isotypes: BISH!, CAS!, MO!, NY!, US!). Description. Herb, terrestrial, stems dark red to red-purple, decumbent or occasionally sub-erect, rooting at nodes, unbranched, rarely 2 - to 3 - branched in the upper part, 3–8 cm long, 1–2 mm in diameter towards the base; internodes 3–5 mm long, densely appressed hirtellous to strigulose, the hairs 0.3–0.5 mm long. Leaves alternate, thinly firm and fleshy, drying chartaceous, ovate, ovate-orbicular, rarely elliptic-ovate, 5–14 (– 18) mm × 4–11 (– 14) mm, palmately 5 - to 7 - nerved, upper surface dull, dark green, moderately appressed hirtellous, lower surface with veins usually dark red to purple, intercostal areas pale pink to red-purple or rarely green, moderately appressed hirtellous, margins revolute, apex acute, base subcordate to rounded or obtuse, rarely cuneate, petioles 2–5 mm long, densely appressed hirtellous. Spikes 1, rarely 2, terminal, 11–17 (– 22) mm long, peduncles red to purple, 4–7 × 0.3–0.4 mm, moderately appressed hirtellous, sometimes densely towards base, the fertile rachis glabrous, yellow-green, 7–14 × 1 mm, flowers moderately congested, bracts orbicular, ca. 0.5 mm diameter, stamens ellipsoidal, 2, ovary ovoid, apex oblique; stigmas terminal, shallowly cleft to bi-lobed. Fruits ovoid, 0.3–0.5 (– 0.8) mm long, dark brown, covered with sticky papillae. Additional specimens examined (paratypes). USA. Hawaiian Islands, Kaua‘i: Kōloa District, • Wahiawa, 670–975 m alt., 13 Apr 1991 (fr.), Flynn et al. 4595 (BISH, PTBG, US) • Kawaihau District, Makaleha Mountains, 823–920 m alt., 2 Jul 1993 (fl. & fr.), Flynn et al. 5398 (PTBG) • Līhu‘e District, Wai‘ahi, 847 m alt., 22 Oct 2020 (fl. & fr.), Wood et al. 18580 (BISH, CAS, PTBG, US). Phenology. Peperomia kauaiana has been observed with flower and fruit during April, July and October. Etymology. The epithet refers to the island of Kaua‘i, oldest and most floristically rich of all the high Hawaiian Islands and the only known location for Peperomia kauaiana. Vernacular name. ‘ Ala‘ala wai nui is the Hawaiian name for related species. Hawaiians used the ash of their burned leaves and stems as a grey-green dye in kapa making (Krauss 2001). Affinities. Lim et al. (2019) presented a phylogenetic analysis of plastomes that indicate four major lineages of Peperomia within the Hawaiian archipelago. Although many relationships within these clades are poorly resolved, additional preliminary analyses, based on recently developed target-enrichment nuclear data using the Angiosperms 353 probe set, corresponds closely with the findings of Lim et al. (2019). The four colonisation events of Peperomia to the Hawaiian Islands represent the largest number of colonisation events of any flowering plant genus to the archipelago (Howarth et al. 1997; Keeley and Funk 2011; Lim et al. 2019). Based on morphological similarity, Peperomia kauaiana belongs to the largest of these radiations, designated as ‘ Hawaiian radiation A’ by Lim et al. (2019). Morphologically, Peperomia kauaiana is most similar to P. degeneri (Moloka‘i, Fig. 5), with both species having very small, strictly alternate leaves that are hirsute to densely hirtellous on both sides, yet P. kauaiana is generally a smaller plant and has revolute rather than flat leaf margins, along with other distinguishing characters noted in the diagnosis. Superficially, P. kauaiana can be confused with P. cookiana C. DC. (Kaua‘i, O‘ahu, Moloka‘i, Lāna‘i, Maui and Big Island of Hawai‘i), as both are relatively small herbs and have hirsute to hirtellous leaves and internodes. However, P. kauaiana has alternate leaves and P. cookiana has opposite or whorled leaves, 2–4 per node. Although P. alternifolia Yunck. (Moloka‘i, Lāna‘i and Maui, Fig. 6 B) and P. oahuensis C. DC. (Kaua‘i and O‘ahu, Fig. 6 C) are alternate-leaved like P. kauaiana, they differ in being entirely glabrous, whereas P. kauaiana has hirsute to hirtellous leaves, petioles, internodes and peduncles. The only other species that could potentially be confused with P. kauaiana is P. latifolia Miq. (Kaua‘i, O‘ahu, Moloka‘i, Lāna‘i, Maui and Big Island of Hawai‘i, Fig. 6 A), yet P. kauaiana differs from P. latifolia in having stem internodes 3–5 mm long, densely appressed hirtellous to strigulose (vs. internodes 10–30 (– 80) mm long, hirsute to subglabrate), leaves strictly alternate 5–14 (– 18) mm × 4–11 (– 14) mm, with revolute margins (vs. leaves alternate, opposite or whorled (20 –) 30–60 (– 75) mm × (15 –) 20–50 (– 65) mm, margins flat), adaxial leaf surface appressed hirtellous (vs. adaxial leaf surface glabrous or hirsute only towards base), petioles 2–5 mm long (vs. petioles 7–20 (– 30) mm long) and spikes 11–17 (– 22) mm long, fertile rachis 1 mm wide (vs. spikes (15 –) 20–80 (– 150) m long, fertile rachis 2–3 mm wide) (see Table 1 and key to Hawaiian Peperomia with alternate leaves). Note: We examined type collections of P. dentulibractea Miq. (Moloka‘i), P. punaluuna C. DC. (O‘ahu), P. villipeduncula C. DC. (O‘ahu) and P. waihoiana St. John (Maui), that were later synonymised with P. latifolia by Yuncker and others (de Condolle 1913; Yuncker 1933; Wagner et al. 1990, 1999) and agree that they fall within the circumscription of P. latifolia. Distribution and ecology. Peperomia kauaiana is endemic to the volcanic island of Kaua‘i where it is has been documented in lowland wet forest around the island’s eastern windward slopes between 670 and 975 m elevation. Location sites include the south-eastern ridges of Wahiawa, the central eastern ridges of Wai‘ahi and the north-eastern ridges of the Makaleha Mountains (Fig. 4). It has predominantly been observed growing terrestrially in layers of bryophytes and in the understorey of ferns. These wet forests are low-statured, range between 3000 and 6500 mm of precipitation per year and are rich in endemic plant species. Dominant genera include trees of Metrosideros Banks ex Gaertn. (Myrtaceae) and Cheirodendron Nutt. ex Seem. (Araliaceae) and large patches of matting ferns, such as Dicranopteris Bernh. and Diplopterygium (Diels) Nakai (Gleicheniaceae). Other common tree and shrub genera include endemic species of Polyscias J. R. Forst. & G. Forst. (Araliaceae); Pritchardia Seem. & H. Wendl. (Arecaceae); Dubautia Gaudich. (Asteraceae); Cyanea Gaudich. (Campanulaceae); Antidesma L. (Phyllanthaceae); Scaevola L. (Goodeniaceae); Hydrangea Gronov. (Hydrangeaceae); Geniostoma (Loganiaceae); Coprosma J. R. Forst. & G. Forst., Kadua Cham. & Schltdl., Psychotria L. (Rubiaceae); and Melicope J. R. Forst. & G. Forst. (Rutaceae). Genera of sedges include Carex L., Cyperus L. and Machaerina Vahl (Cyperaceae). Smaller shrubs, herbs and vines include Astelia Banks & Sol. ex R. Br. (Asteliaceae); Bidens L. (Asteraceae); Vaccinium L. (Ericaceae); Cyrtandra J. R. Forst. & G. Forst. (Gesneriaceae); Freycinetia Gaudich. (Pandanaceae); and Smilax L. (Smilaceae). Occasional genera of ferns include Sadleria Kaulf. (Blechnaceae); Cibotium Kaulf. (Cibotiaceae); and Microlepia C. Presl (Dennstaedtiaceae). Other Peperomia species in the nearby vicinity of P. kauaiana include three predominantly terrestrial species, P. cookiana, P. hesperomannii Wawra and P. latifolia (Fig. 6 A), along with one epiphytic species, P. oahuensis (Fig. 6 C). Key to Hawaiian Peperomia with alternate leaves Note: H = Hawai‘i (Big Island); K = Kaua‘i; L = Lāna‘i; M = Maui; Mo = Moloka‘i; O = O‘ahu. Preliminary conservation assessment. IUCN Red List Category. When evaluated using the World Conservation Union (IUCN) criteria for endangerment (IUCN 2012, 2024), Peperomia kauaiana falls into the Critically Endangered (CR) category, indicating a high risk of extinction in the wild. Our formal evaluation can be summarised by the IUCN hierarchical alphanumeric numbering system of criteria and subcriteria, CR B 1 ab (iii) + 2 ab (iii), which reflects a severely limited extent of occurrence (EOO) of 12 km 2, an area of occupancy (AOO) of less than 4 km 2, a wild population of only three small sub-populations consisting of 1500–2100 mature plants and a continuing decline in the quality of habitat inferred. The continued decline in quality of habitat for P. kauaiana is evidenced by severe habitat degradation from invasive non-native mammals, such as pigs (Sus scrofa L.), rats (Rattus spp.) and occasional goats (Capra hircus), along with introduced slugs, insects and disease. Other serious threats include hurricane-force winds, flash floods, landslides triggered after torrential rains and invasive non-native plants that displace naturally occurring ones within P. kauaiana habitat, especially Sphaeropteris cooperi (Hook. ex F. Muell.) R. M. Tryon (Cyatheaceae); Melastoma septemnervium Lour., Miconia crenata (Vahl.) Michelang. (Melastomataceae); Psidium cattleyanum Sabine, Rhodomyrtus tomentosa (Aiton) Hassk. (Myrtaceae); Axonopus fissifolius (Raddi) Kuhlm. (Poaceae); Rubus rosifolius Sm. (Rosaceae); and Buddleja asiatica Lour. (Scrophulariaceae). Notes on two possibly extinct Hawaiian Peperomia Plant and animal endemics from isolated oceanic islands are more often critically endangered and highly susceptible to extinction, being particularly vulnerable and sensitive to invasive introducti