taxonID	type	description	language	source
6C345A09A9E153078B1B4D7AEC5D749B.taxon	description	Figs 1, 2, 3 A – C, 4	en	Wood, Kenneth R., Wagner, Warren L., Fawcett, Susan (2026): Peperomia kauaiana (Piperaceae), a new alternate-leaved species from Kaua‘i, Hawaiian Islands and notes on two possibly extinct Hawaiian Peperomia. PhytoKeys 269: 113-129, DOI: 10.3897/phytokeys.269.173971
6C345A09A9E153078B1B4D7AEC5D749B.taxon	diagnosis	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).	en	Wood, Kenneth R., Wagner, Warren L., Fawcett, Susan (2026): Peperomia kauaiana (Piperaceae), a new alternate-leaved species from Kaua‘i, Hawaiian Islands and notes on two possibly extinct Hawaiian Peperomia. PhytoKeys 269: 113-129, DOI: 10.3897/phytokeys.269.173971
6C345A09A9E153078B1B4D7AEC5D749B.taxon	description	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.	en	Wood, Kenneth R., Wagner, Warren L., Fawcett, Susan (2026): Peperomia kauaiana (Piperaceae), a new alternate-leaved species from Kaua‘i, Hawaiian Islands and notes on two possibly extinct Hawaiian Peperomia. PhytoKeys 269: 113-129, DOI: 10.3897/phytokeys.269.173971
6C345A09A9E153078B1B4D7AEC5D749B.taxon	etymology	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.	en	Wood, Kenneth R., Wagner, Warren L., Fawcett, Susan (2026): Peperomia kauaiana (Piperaceae), a new alternate-leaved species from Kaua‘i, Hawaiian Islands and notes on two possibly extinct Hawaiian Peperomia. PhytoKeys 269: 113-129, DOI: 10.3897/phytokeys.269.173971
6C345A09A9E153078B1B4D7AEC5D749B.taxon	distribution	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 introductions of foreign plants and animals (Milberg and Tyrberg 1993; Kearns et al. 1998; Sakai et al. 2002; Wood 2012; Wood et al. 2019). The loss of suitable habitat on islands can be devastating to specialised species, especially considering their inherently limited land mass when compared to continental regions (Heinen et al. 2018). Currently, there are over 130 Hawaiian vascular plant taxa that are considered possibly extinct, including two Hawaiian Peperomia species, namely P. degeneri from Moloka‘i (Fig. 5) and P. subpetiolata Yunck. from Maui (Fig. 7) (Wood 2012; Wood et al. 2019). The following is a summary of where and when those two Peperomia species were observed and we encourage efforts be made to relocate them. Peperomia degeneri (Fig. 5) has only been documented from two locations (Fig. 8). It was originally collected by O. Degener in 1928 on shaded cliffs along the east arm of Kalua‘aha Valley, Moloka‘i at an unrecorded elevation and was subsequently described by Yuncker in 1933. For many years, botanists studying the Hawaiian flora lost track of any wild populations and considered P. degeneri to be possibly extinct. Its re-discovery occurred in 2008, 80 years after Degener’s observation, when H. Oppenheimer made an herbarium collection around Waihānau Valley, Moloka‘i, at an elevation of 900 m. Unfortunately, when Oppenheimer returned to the site several years later, the colony of P. degeneri had perished, once again raising the possibility of its extinction. It should be noted that, although Yuncker (1933) describes the spike of Peperomia degeneri as being up to 3 cm long, on careful examination of the isotype collections, we find that the spike (peduncle and fertile rachis) can be as long as 4.8 cm (see diagnosis and key to Hawaiian Peperomia with alternate leaves). It is also worth noting that P. degeneri has only been documented on vertical habitats, with Degener having found it on shaded cliffs and Oppenheimer on vertical stream banks. Specimens of Peperomia degeneri examined. USA. Hawaiian Islands, Moloka‘i: • Kalua‘aha Valley, 12 Jul 1928 (fl., fr.), Degener and Wiebke 3061 (isotypes: BISH, CAS, ILL, K, MASS, NY, RM, US) • Waihānau, 900 m alt., 25 Sep 2008, (fl., fr.), Oppenheimer H 90814 (BISH). Peperomia subpetiolata (Fig. 7) is a rare species on East Maui, known only from a small area near and along Olinda Road. This area is just west of the Makawao / Koolau forestry boundary line (Fig. 9). It is a highly distinctive Hawaiian species with leaves 5 – 8 per node, up to 20 cm long, linear-lanceolate to narrowly elliptic and a spike with a rachis 3.5 – 4 mm in diameter. Only 11 collections are known and were made in the general area of the Kula Pipeline and Waikamoi Road. No pure individuals of P. subpetiolata have been recorded since the late 1990 s and only putative hybrids have been observed since then, most likely between P. subpetiolata × P. cookiana and / or P. subpetiolata × P. hirtipetiola. Peperomia kulensis Yunck. originally described in 1933, based on a single specimen collected from below Kula pipeline on East Maui (G. Munro 800 (BISH )) was treated as a synonym of P. subpetiolata by Wagner et al. (1990, 1999). The features that differed in the type and only collection were included within the description of P. subpetiolata by Wagner et al. (1990, 1999), primarily plant parts hirsute, leaves 9 - to 11 - nerved and the petiole more distinct, but narrowly winged. In 1995, the type was re-examined by Joel Lau and Wagner with the knowledge that P. hirtipetiola C. DC. also grew in those areas and concluded the type was most likely a hybrid and thus annotated the type as a putative hybrid P. subpetiolata × P. hirtipetiola. Since this putative hybrid is now removed from inclusion in P. subpetiolata, a new description is needed and is provided below. Description. Herb, terrestrial, stems greenish with reddish-purple splotches, erect to ascending from a very short repent base, not rooting at the nodes, stout, unbranched or 2 - or 3 - branched in upper part, ca. 60 – 150 cm long, 8 – 20 mm in diameter, internodes 3 – 4 cm long or up to 12 cm long in lower part of stem, glabrous. Leaves 5 – 8 per node, relatively thin, coriaceous, drying chartaceous, linear-lanceolate to narrowly elliptic, 12 – 20 cm long, 1.5 – 4 cm wide, palmately 5 - nerved, veins impressed on upper surface, upper surface dark green, lower surface pale green, glabrous, apex long-acuminate, base attenuate, tapering to a short narrowly winged petiole, 0.2 – 1 cm long. Spikes 1 to 3, terminal and axillary, 8 – 12 cm long, peduncles ca. 2 – 3.5 cm long, 3.5 – 4 mm in diameter, glabrous, flowers densely congested; stamens ellipsoidal, 2; ovary turbinate; stigmas terminal, inconspicuously divided. Fruit subglobose, ca. 1 mm in diameter. Specimens of Peperomia subpetiolata examined. USA. Hawaiian Islands, East Maui: • Waikamoi, Kula Pipeline, 5 Sep 1919, Forbes 1283. M (holotype: BISH) • loc. cit., 1372 m alt., 11 Feb 1930, St John 10299 (BISH) • loc. cit., 1250 m alt., 14 Mar 1984, Hobdy 2017 (BISH) • loc. cit., 1250 m alt., 29 Oct 1986, Hobdy 2635 & 2636 (BISH) • loc. cit., 1250 m alt., 14 Mar 1984, Wagner et al. 5675 (BISH).	en	Wood, Kenneth R., Wagner, Warren L., Fawcett, Susan (2026): Peperomia kauaiana (Piperaceae), a new alternate-leaved species from Kaua‘i, Hawaiian Islands and notes on two possibly extinct Hawaiian Peperomia. PhytoKeys 269: 113-129, DOI: 10.3897/phytokeys.269.173971
