Pacifigeron indivisus Saldivia, 2020

Saldivia, Patricio, Wood, Kenneth R., Orlovich, David A. & Lord, Janice M., 2020, Pacifigeron indivisus (Asteraceae: Astereae), a new species endemic to Rapa, Austral Islands, and a new delimitation of the Celmisia group, Phytotaxa 442 (4), pp. 239-266 : 253-257

Pacifigeron indivisus Saldivia , sp. nov. ( Fig. 3A–C , 4 , 5 ).

Type: — FRENCH POLYNESIA. Rapa : Anarua, ridge system below and south of Perau-Namuere summit, running north-south, 223 m, 7 May 2002, K. R. Wood 9763 (holotype PTBG 41324!).

Diagnosis: — P. indivisus differs from P. rapensis by its larger leaves of 16–21 × 5–9 cm (vs 2–5 × 1.2–2.7 cm), capitula arranged in dense compact panicles (vs capitula arranged in loose umbeliform capitulescences), disciform capitula (vs radiate capitula), and the undivided style of the disc florets (vs style divided in two branches).

Small tree 1–2 m tall. Stems stout, terete, transversally marked by the scars of the past leaves, 3–4 times branched, tan-brown. Leaves alternate, clustered at the distal part of the branches, glabrescent or with some persistent scattered multicellular, uniseriate, unbranched, eglandular trichomes, 1.5–2.5 mm long, which are wider at the bottom tapering toward the apex, and strongly curved towards the leaf apex ( Fig. 5H ), broadly obovate-spatulate, (14–)16–21 × (4–) 5–9 cm, coriaceous, lustrous, serrate, double-serrate, or untoothed (near the base or completely), flat or slightly undulate, tapering to a broad pseudo-petiolar and semi-clasping base with a dense and persistent clump of white-villous eglandular, linear, unbranched, uniseriate, multicellular (with elongated cells slightly dilated in the junctions) trichomes, 4–6 mm long, arising from the axil, venation deeply impressed on the adaxial surface and raised on the abaxial surface, midvein white, wider at the base (4–7 mm), tapering towards the apex and becoming abruptly thinner (as the second-order veins) from about the center of the leaf and finally anastomosed, secondary veins (5–6) arising from the bottom half of the leaf, running parallel and relatively equally spaced to each other and following the margin, becoming diffuse and anastomosing near the margin. Capitula disciform, 6–7 × 5–6 mm, campanulate to urceolate, sessile or subsessile in short peduncles ca. 5 mm long, forming a dense terminal paniculate cluster composed of 60–80 capitula. Phyllaries arranged in 3(–4) series, glabrous, pale green, the external ones shorter and wider than the inner ones, fimbrillate near the apex, external ones 4.5 × 1.5 mm, oblong-lanceolate, shortly acuminate, with well-developed mid and secondary veins forming a reticule at the base; mid phyllaries 5–5.5 × 1 mm, lanceolate, shortly acuminate, only midvein developed with two faint secondary veins to each side; inner phyllaries 6 × 0.8 mm, linear-lanceolate with a long acumen and midvein developed. Receptacles 3 mm wide, nearly flat to slightly concave, epaleate, slightly alveolate. Ray florets ca. 30 in 2–4 series, pistillate, fertile; corolla 7–8 mm long, broadened at the transitional area between the tube and limb, with some scattered eglandular biseriate trichomes 150–200 μm ( Fig. 5G ) grouped mainly around the end of the tube ( Fig. 5E ), tube cylindrical, 3.5–4 mm long, limbs 3.5–4 × 0.8 mm, linear, irregularly 3- lobed, although some of the florets present a totally suppressed limb resulting in only a short filiform corolla (tube), white; style conspicuously exserted, 7–10 mm long, style branches diminutive, 100–200 μm long. Disc florets ca. 12, functionally staminate, sterile ovaries 3 mm long; corolla infundibuliform, 6.5–7 mm long, 5-lobed, lobes 1 mm long, with some scattered eglandular trichomes (as in the ray florets) chiefly towards the corolla opening and lobes, white-yellowish or with light green tinge; style 8–8.5 mm long, unbranched, completely undivided ( Fig. 4 ), with papillae covering its whole length, stigmatic bands absent; stamens ca. 3 mm long, anthers 1.2 mm long, basally attenuate, obtuse, apical appendage 300 μm long, acute, filament collar 200 μm long, swollen, twice the width of the filament; pollen grains equinulate, 20 μm diameter. Cypselae slightly compressed, laterally asymmetrical, slightly gibbous, 2.5– 3 × 1–1.3 mm, with 9–11 raised, longitudinal, nearly equally spaced ribs, glabrous, dark brown. Pappus of numerous bristles arranged in 2(–3) series of approximately the length of the tube (3.5–4 mm) in the ray florets and ca. 2 mm long (1/3 of the corolla length) in the disc florets, the two inner series forming a basal ring, and some scattered shorter setae forming an outer row.

Phenology: —Specimens in flower have been collected in March, April, and May; mature cypselae collected in May.

Etymology: —The specific epithet refers to the distinctive undivided style of the disc florets.

Distribution, habitat, and ecology: — Pacifigeron indivisus has only been recorded in three localities of northwestern Rapa ranging between 223 and 579 m, with a total estimated population of ca. 275 mature individuals. To date, the largest subpopulation, consisting of ca. 200 mature plants and 100 seedlings, was observed at 223 m along the Anarua ridge system, to the south of Perau summit ( Fig. 1 ). This site has a steep 20–50° slope, a 30–40% open canopy, and occurs just below an exposed windy ridge. Approximately ten individuals of P. rapensis were also observed on exposed windy ridges around this locality. The surrounding plant community is a mixture of wet shrubland and forest associated with large patches of the woody climber Freycinetia arborea . The substrate is consistent in all three subpopulations, noted as being brown silty soil with basalt talus. The local habitat is interspersed with trees of Corokia collenettei , Eurya rapensis , Fitchia nutans , F. rapensis , Metrosideros collina , Oparanthus coriaceus , Pittosporum rapense , Veronica rapensis , and scattered trees of the large-leafed Meryta choristantha . The large terrestrial fern, Sphaeropteris medullaris is common, some with caudex exceeding three m. Other smaller ferns, both terrestrial and epiphytic are Abrodictyum dentatum , Alsophila stokesii , Asplenium caudatum , Elaphoglossum rapense , Grammitis maireaui , Loxogramme parksii , Parablechnum pacificum , P. vestitum , and Thelypteris diversisora .

The second largest subpopulation of P. indivisus consists of ca. 70 mature individuals and occurs between 366 and 396 m around the Namuere region ( Fig. 1 ), to the north of Mt Perau summit. This subpopulation grows just below a primary ridge on a slope of 20° and continues to do well on increasingly steep slopes of 60°. The canopy is 40–70% open and the plant community is a mixed wet forest interspersed with fernland-shrubland and dominated by Freycinetia arborea and Corokia collenettei . Most of the associated trees found in the Anarua ridge subpopulation were also present in the Namuere region, but this locality also includes trees of Phyllanthus longfieldiae , along with shrubs of Vaccinium rapae and Plantago rupicola . Conspicuous endemic sedges around Namuere include Carex stokesii and Rhynchospora stokesii . Ferns dominated the terrestrial understory zone including many epiphytes and lithophytes interwoven with mosses, lichens, and liverworts. Fern and lycophyte species in their order of dominance includes numerous species of small epiphytic Hymenophyllum , and medium sized ferns such as Alsophila stokesii , Asplenium caudatum , A. gibberosum , A. lucidum , A. nidus , Belvisia dura , Blechnum attenuatum , Christella parasitica , Cranfillia vulcanica , Davallia solida , Elaphoglossum rapense , E. samoense , Histiopteris incisa , Lycopodium squarrosum , Parablechnum venosum , Pteris comans , Selaginella arbuscula , Sphaeropteris medullaris , and Thelypteris margaretae .

A third colony of P. indivisus consisting of five individuals was observed at 579 m in a small drainage on Mt Perau’s southern face ( Fig. 1 ). These plants occurred along a gentle 20° slope at the forest edge, open to light ca. 70% of the day. It is interesting to note that ca. 30 indiviuals of P. rapensis were observed on an exposed windy mosscovered ridge right above this site. The surrounding habitat is considered tropical montane cloud forest (TMCF), a very rare community that is restricted to small isolated patches above 550 m on Rapa ( Meyer 2010) . The TMCF community around the Mt Perau summit is of extraordinary interest, considering its extreme biological diversity. Small side drainages of clean cascading waters were abundant with numerous species of skimming Diptera , flightless weevils, longhorned beetles, fulgoroid planthoppers, Lepidoptera , and a rich diversity of terrestrial molluscs. During this 2002 survey, 20 individuals of the endemic Rapan fruit dove ( Ptilinopus huttoni ), were also observed around the Mt Perau TMCF summit. Known by the local people as koko, the second author estimated ca. 200 of these rare fruit doves remaining on Rapa (K. Wood, unpublished data), most likely still surviving because of the absence of black rat ( Rattus rattus ).

The TMCF habitat where P. indivisus occurs is dominated by Freycinetia arborea , Metrosideros collina , and Corokia collenettei . Associate tree species include Acalypha rapensis , Apetahia margaretae , Celtis pacifica , Claoxylon collenettei , Coprosma cookei , Eurya rapensis , Fitchia nutans , Geniostoma rapense , Homalanthus stokesii , Meryta choristantha , M. pauciflora , Myrsine rapensis , Oparanthus coriaceus , O. rapensis , Phyllanthus longfieldiae , Pittosporum rapense , Psychotria rapensis , Streblus anthropophagorum , and Weinmannia rapensis . Smaller shrubs and herbs included Astelia rapensis , Haloragis stokesii , Kadua rapensis , Macropiper puberulum , Peperomia rapensis , Pilea occulta , Plantago rupicola , Vaccinium rapae , and Veronica rapensis . Of unique floristic interest, Haroldiella rapaensis , a French Polynesian endemic dioecious genus in the nettle family also proliferates along shady, closed-canopy stream banks. The diversity of terrestrial and epiphytic pteridophytes and lycophytes in the TMCF is great for such a small area and associated with a proliferation of bryophytes. Both palm-like emergent tree ferns, Alsophila stokesii and Sphaeropteris medullaris , are conspicuous throughout the TMCF along with large specimens of Angiopteris rapensis . Other notable fern taxa are Abrodictyum caudatum , A. dentatum , Asplenium caudatum , A. gibberosum , A. nidus , A. polyodon , Athyrium tenuipaleatum , Blechnum attenuatum , Callistopteris calyculata , Calymmodon rapensis , Cranfillia vulcanica , Davallia fejeensis , D. solida , Diplazium rapense , Doodia media , Elaphoglossum rapense , Elaphoglossum samoense , a narrow-leafed form of Haplopteris elongata , Histiopteris incisa , Hymenophyllum polyanthos , Hypolepis tenuifolia , Lycopodium squarrosum , L. venustulum , Microsorum dilatatum , Parablechnum venosum , Pneumatopteris stokesii , Polystichum stokesii , Pteris comans , P. tripartita , and Selaginella arbuscula . There are occasional vines of Alyxia stellata , and an abundance of terrestrial sedges such as Carex stokesii , Cyperus rapensis , and Rhynchospora stokesii , along with an undescribed species of Carex sect. Uncinia .

Conservation Status: — Under the criteria for endangerment used by the World Conservation Union ( IUCN 2001), P. indivisus falls into the Critically Endangered (CR) category, which designates this species as facing the highest risk of extinction in the wild. Our evaluation can be summarized by the following IUCN hierarchical alphanumeric numbering system of criteria and subcriteria: B1ab(iii); B2ab(iii). These criteria are defined as: B1, extent of occurrence less than 100 km 2; B1a, subpopulations severely fragmented; B1b(iii) continuing decline inferred in the quality of habitat; B2, area of occupancy less than 10 km 2; B2a, subpopulations severely fragmented; B2b(iii), continuing decline inferred in the quality of habitat. Habitat threats throughout the range of P. indivisus include degradation by introduced herbivores, especially feral goats which were observed right up to the summit region of Mt Perau, and cattle; competition with non-native plant species, especially Psidium cattleyanum , Rubus rosifolius , and Syzygium jambos ; climate change; fire; devastation by severe storms; inbreeding depression as the result of limited numbers of individuals; and the introduction of potentially lethal plant diseases.

Additional specimens examined (paratypes): — FRENCH POLYNESIA. Rapa : Namuere region , trail to Perau, 366 m, 28 March 2002, K. R. Wood 9462 ( PTBG 66486 ) ; Namuere , along trail up to Perau, 396 m, 8 May 2002, K. R. Wood 9778 ( PTBG [70% Ethanol]) .

Additional specimens collected in 2002: — Several collections of P. indivisus made by K.R. Wood in 2002, including duplicates of the specimens kept at PTBG, were sent directly to NY from Rapa . Dr. Timothy Motley, working at that time on molecular systematics at NYBG, was the lead researcher of the 2002’s Rapa expedition and was in charge of sorting the collections to different herbaria including NY. Regrettably, Dr. Motley passed away in March 2013 and staff from NY herbarium have been unable to locate them.

These collections are as follows:— FRENCH POLYNESIA. Rapa : Perau, summit and adjacent drainages just below, 579 m, 30 March 2002, K. R. Wood 9468 (field images, see Fig. 3A ) ; Namuere , along trail up to Perau, 396 m, 5 April 2002, K. R. Wood 9570 .

Figures

FIGURE 1. Distribution map of Rapa, the Celmisia group, and some of the genera discussed in the text. Inset: Pacifigeron rapensis (circles) and P. indivisus (triangles). Distribution of other South American genera mentioned in the text are almost totally included within the distributions of Diplostephium and Linochilus. Laennecia is also distributed in southwestern USA and Mexico.

FIGURE 3. Pacifigeron indivisus. A. Capitulum. B. Terminal capitulescence of many clustered capitula. C. Habit. P. rapensis. D. A few individuals (note the terminal capitulescences of few capitula). E. Habit. Photographs: A by Kenneth R. Wood, B–E by Jean-Yves Meyer.

FIGURE 4. Detail of the undivided style apex of the disc floret of Pacifigeron indivisus Scale bar: A = 500 µm, B = 100 µm.

FIGURE 5. Pacifigeron indivisus. A. Disc floret. B. Style branches of the ray floret. C. Ray floret with the front part of the pappus removed. D. Cypsela and pappus from the ray floret. E. Back and lateral view of the corolla of the ray floret showing concentration of trichomes around the area between tube and limb. F. Androecium. G. Eglandular biseriate trichomes from the corolla (disc and ray). H. Multicellular, uniseriate, unbranched, eglandular trichomes from the leaves. I. Phyllaries from left to right: external to internal. J. Abaxial surface of the leaf margin. K. Leaf (adaxial surface). Scale bar:A, C–F, H–I = 1 mm, B, G = 100 µm, J–K = 1 cm. Drawn from K.R. Wood 9763 (PTBG) and K.R. Wood 9462 (PTBG) by Patricio Saldivia.