Pogostemon guamensis Lorence & W.L.Wagner, 2020

Lorence, David H., Wagner, Warren L., Wood, Kenneth R. & Johnson, Gabriel, 2020, Pogostemon guamensis Lorence & W. L. Wagner (Lamiaceae), a new species from Guam, Mariana Islands, PhytoKeys 169, pp. 61-73 : 61

Pogostemon guamensis Lorence & W.L.Wagner sp. nov. Figures 2 , 3

Type.

Mariana Islands. Guam: Yigo Municipality. Andersen Air Force Base, Pati Point, just west of point, 10 degrees north aspect, 2 July 1994, S. P. Perlman & K. R. Wood 14266 (Holotype PTBG 061045!; Isotypes BISH!, GU!, K!, NY!, UC!, US!).

Diagnosis.

Shrub or subshrub growing on limestone cliffs, distinguishable from its congeners by its non-aromatic parts; inflorescence a loose thyrse, 2.5-5 cm wide and up to 7 cm wide in fruit; calyx equally 5(6)-toothed, externally densely hirtellous and internally glabrous; corolla white, weakly bilabiate, tube 8-10 mm long, externally sparsely white pilosulous in distal half, glabrous in basal half, internally pilosulous up to base of lobes; stamens long-exserted with filaments 13-14 mm long, bearded with septate, non-moniliform trichomes in basal half and glabrous in distal half or occasionally with trichomes along entire length, with anthers reniform, 0.4 mm long; style plus stigma ca. 15-16 mm long, stigma lobes 2, equal, linear, 1.6-2.2 mm long.

Description.

Diffusely branching, non-aromatic perennial shrub or subshrub 75-130 cm tall, main stem to 2 cm diameter at base, bark pale brown, a pair of branches usually developing below each inflorescence, mature stems solid, weakly 4-angled, 3-3.2 mm wide, 4-sulcate, yellowish green when fresh, drying brown, stems, petioles, and inflorescences densely hirtellous with brown, patent, multicellular, non-glandular, 4-6-celled trichomes 0.1-0.2 mm long mixed with shorter capitate glandular trichomes <0.1 mm long. Leaves opposite, when fresh somewhat fleshy, yellowish green adaxially, paler abaxially, drying brown, chartaceous, blade broadly ovate to ovate-cordate, (4.5-)6-13.5 cm long, (3.5-)5-8.5 cm wide, adaxially uniformly hirtellous with antrorsely curved pale brown or whitish hairs 0.2-0.3 mm long, abaxially similarly hirtellous but with hairs denser on midrib, veins, and margin, surface densely yellowish-brown glandular punctate, margin serrate-crenate or biserrate-crenate, teeth obtuse, 0.4-1 cm apart, apex acute to short acuminate, the acumen to 1 cm long, base cordate to subcordate or sometimes truncate and rounded, secondary veins (4)5-6 on each side, basal pair arising near petiole insertion, tertiary venation reticulate, prominulous on both surfaces; petiole (2-)4-7 cm long, 1.2-1.5 mm wide, densely brown hirtellous. Inflorescence terminal, a single loose, densely flowered, cylindrical thyrse (3-)4.5-19 cm long, 2.5-5 cm wide, elongating to 20 cm long and 7 cm wide in fruit, when fresh yellowish green, densely hirtellous, peduncle (4-)10-15 mm long; flowers (25-) 50 to several hundred (rarely to ca. 700) per inflorescence; opposite cymes sessile or on peduncle 2-3 mm long, occasionally subtended by a narrowly triangular-subulate bract 3.5-6 mm long, cymes usually branched once, each branch (3-)6-20-flowered, rachis slightly undulating or zig-zag, elongating to 35 mm in fruit; flowers secund, on pedicel 0.5-2 mm long, subtended by (1-)2 narrowly subulate bracteoles 1-1.2 mm long; calyx radially symmetrical, equally 5(6)-toothed, externally densely hirtellous with patent or slightly ascending non-glandular trichomes, tube 4.5-6 mm long, obconic-cylindrical, 10(12)-veined, internally glabrous, teeth equal to slightly subequal, narrowly triangular-acute, 1.5-2.5 mm long, 0.8-1 mm wide at base, with distinct mid and marginal vein, densely hirtellous on both surfaces with scattered sessile glands; corolla white, venose when dry, exserted from calyx, funnelform, tube 8-10 mm long, slightly gibbous at base, 0.7- 0.8 mm wide medially, 2-3 mm wide at apex of tube, 2-lipped, upper lip 3-lobed, lobes obtuse, ca. 1.3 mm long and wide, lower lip entire, 1.8-2 mm long, corolla tube externally sparsely white pilosulous in distal half, glabrous in basal half, internally pilosulous up to base of lobes; stamens 4, exserted 5-7 mm beyond corolla lobes, attached ca. 2-3 mm from base of tube, filaments 13-14 mm long, sparsely villous bearded in basal half with white septate (non-moniliform) trichomes and glabrous in distal half or occasionally with trichomes along entire length; anther reniform, 0.4 mm long; style terminal, glabrous, exserted, slightly longer than stamens, style plus stigma ca. 15-16 mm long, stigma lobes 2, equal, linear, 1.6-2.2 mm long. Nutlets 4, ellipsoid, smooth, c. 0.3 mm long, 0.2 mm wide (immature), mature nutlets not seen, said to be brown-black (Wood 3370, PTBG).

Distribution.

Known only from the karstic limestone cliffs of northeastern Guam, Mariana Islands.

Phenology.

Flowers were collected in April and July and immature fruit in July. In the many of the specimens examined flowers and nutlets had been eaten by herbivorous insects in the field, and consequently mature nutlets were not available for study.

Habitat and ecology.

The northern end of Guam is characterized by a reef-associated limestone plateau that has been uplifted above sea level and flanked by cliffs that can exceed 190 m (c. 600 ft) high (Fig. 4 ). The forests growing on the elevated limestone plateau surrounding Andersen Air Force Base (AAFB) contain some of the richest native plant communities on Guam, although the forests and cliff habitat are often impacted by severe typhoons. The sharp, treacherously jagged karstic limestone makes it extremely dangerous for exploration and rappelling with ropes.

Pogostemon guamensis is known only from the dry to mesic karstic limestone cliffs of northeastern Guam at 370-550 ft (113-168 m) elevation, with small groupings occurring between Lafac Point to the south and the Tarague cliffs to the north. The coastal cliff community is dominated by halophytic scrub vegetation with woody species such as Aglaia mariannensis Merr., Bikkia tetrandra (L.f.) A. Rich., Eugenia bryanii Kaneh., E. palumbis Merr., E. reinwardtiana (Blume) DC., Excoecaria agollocha L., Ficus prolixa G. Forst., Guamia mariannae (Safford) Merr., Leptopetalum foetidum (G. Forst.) Neupane & N. Wikstr., Macaranga thompsonii Merr., Meiogyne cylindrocarpa (Burck) Heusden, Ochrosia mariannensis A. DC., Pemphis acidula J.R. Forst. & G. Forst., Phyllanthus mariannensis W. L. Wagner & Lorence, P. marianus Muell.-Arg, Pipturus argenteus (G. Forst.) Wedd., Polyscias grandifolia Volkens, Premna serratifolia L., Psychotria mariana Bartl. ex DC., Scaevola taccada (Gaertn.) Roxb., Syzygium thompsonii (Merr.) N. Snow, Triphasia trifolia (Burm.f.) P. Wilson, and Wikstroemia elliptica Merr., with associated herbaceous species including Cassytha filiformis L., and Peperomia mariannensis A. DC. Invasive alien plant species competing with the new species include Chromolaena odorata (L.) R.M. King & H. Rob., Passiflora suberosa L., Sporobolus farinosus Hosok., and Triphasia trifolia (Burm.f.) P. Wils. Feral pigs ( Sus scrofa ) and the introduced Philippine or sambar deer ( Rusa marianna ) are also serious threats to the surrounding habitat, in addition to wind damage from severe typhoons.

Conservation status.

During separate cliff rappels five subpopulations ranging in size from 1 to 30-50 plants were observed on vertical cliff faces, for a total of 113 individuals observed ( Perlman and Wood 1994) (Fig. 5 ). Based on the IUCN categories and criteria this species is assigned a preliminary Red List status of Critically Endangered (CR) based on its AOO of <10 km² (i.e., 4 km²) and its EOO of <100 km² (i.e., 4 km²), and it has only one known location, with continuing decline in both AOO and EOO inferred.

Specimens examined

(Paratypes). Mariana Islands: Guam: Yigo Municipality. Pati Point, ca. 500 ft., edge of limestone cliff, 14 April 1982, D. Herbst 6656 (BISH); Andersen Air Force Base, Pati Point area; 400-600 ft., N aspect. 2 July 1994, K. R. Wood 3300 (BISH, CAS, GU, MBK, NY, P, PTBG [2], US, WU); Andersen Air Force Base, near Tarague, steep cliffs around beach access road, 137 m, 18 Jul 1994, K. R. Wood 3370 (GU, PTBG, P, US); Andersen Air Force Base, Pati Pt., 350 degrees north aspect, rappel between 400-600 ft., 9 July 1994, K. R. Wood & S. P. Perlman 3359 (GU, PTBG, US); Andersen Air Force Base, just north of Latte Point, between Latte and Pati Point, 5 July 1994, S. P. Perlman 14289 (GU, PTBG, MO, US); Andersen Air Force Base, west of Tagua, 400-550 ft., 330 deg. asp., 7 July 1994, K. R. Wood & S. P. Perlman 3337 (GU, PTBG); Andersen Air Force Base, west of Tagua, between Tagua and Tarague, off Crow Transect 9, on cliff, 7 July 1994, S. P. Perlman & K. R. Wood 14295 (GU, PTBG).

Figures

Figure 2. Pogostemon guamensis Lorence and W. L. Wagner A habit, stem with leaves and inflorescence B detail of abaxial leaf surface showing pubescence and sessile glands C portion of inflorescence showing cymes with calyces and four corollas D calyx E corolla at anthesis F corolla, opened along one side G gynoecium with portion of calyx removed showing ovary and style. Drawn from Perlman and Wood 14295 (A, B), Wood and Perlman 3359 (C-E), and Wood and Perlman 3300 (F, G). Illustration by Alice Tangerini.

Figure 3. Pogostemon guamensis Lorence and W. L. Wagner (Perlman & Wood 14266, holotype PTBG- 061045).

Figure 4. Coastal limestone cliffs of NE Guam, photo courtesy of Toni Mizerek.

Figure 5. Distribution map showing five known localities for Pogostemon guamensis on NE part of Guam.