Sagina hookeri Timaná & Lebouvier & Rouhan 2019, sp. nov.

Sagina hookeri Timaná, sp. nov. (Figs 2; 3; 4)

Sagina hookeri Timaná, sp. nov. is morphologically close to Sagina diffusa (Hook.f.) Timaná but differs in its caespitose life form, much smaller overall size, and wide obtuse petals.

TYPUS. — Terres australes et antarctiques fran ç aises. District de Saint-Paul et Amsterdam, Île Amsterdam, Del Cano, Terres Rouges,

37°52’26”S, 77°32’23”E, alt. 48 m, 16.XII.2016, G. Rouhan, D. Ertz, J. Mieusset, C. Ollive, B. Van de Vijver 1841 (holo-, P[P02434524]!).

ADDITIONAL SPECIMENS EXAMINED. — Terres australes et antarctiques fran ç aises. Île Amsterdam, Plaques terreuses sur coulée basaltique près du Camp, 15.XII.1963, A. Lourteig et P. Cour 57, (P [P04937011]!); Haut de la falaise de la Pearl, 13.III.1970, P. Noël s.n. (P [P00915539]!); Cratère Hébert, alt. 180 m, 26.I.1985, J.-C. Jolinon 1060 (P [P04937000]!).

PHENOLOGY. — Found flowering and fruiting from December to March (austral summer).

DESCRIPTION

Caespitose, compact herb; plant upright, 1.2-3.0 cm high (including inflorescence). Leaves opposite, sometimes arching backwards, fleshy, glabrous, sessile, lanceolate, 5.2-8.8 mm long; apex acute, mucronate; midvein barely noticeable; surface smooth, shiny, margin entire. Inflorescences axillary, flowers solitary, pedicel 5.6-9.2 mm long, glabrous, upright even during fruit dehiscence, green to pale green. Flowers tetramerous, rarely pentamerous; sepals 4(5), imbricate, cymbiform, broadly ovate, 1.9-2.8 mm long, 1.1-1.5 mm wide, margins slightly hyaline, apex obtuse, green then turning pale yellow when fruiting, shorter or almost as long as capsule valves, persistently appressed to valves; petals present, 4(5), alternisepalous, thin, white, orbicular, apex wide obtuse to truncate, with a short claw at the base, much shorter than sepals, 1.3- 1.5 mm long, 0.8 mm wide, probably deciduous after anthesis; stamens episepalous, as long as petals. Fruit a 4(5)-valved multiseeded capsule, 2.3-3 mm long, pale yellow at maturity, with valve apices arching backwards when mature; seeds blackish.

REMARK

The specimens collected by P. Cour (Cour s.n., s.d. [P04937002!] and E. Aubert de la Rue s.n. [P04937003!]) may also belong to the new species described here, however, their limited quality does not allow a definitive assessment. The specimen A. Lourteig & P. Cour 67 (P04938223!) is supposed to have been collected in Kerguelen Island, according to the printed label added after the gathering arrived at the P herbarium. By contrast, the original la- bel handwritten by the collectors does not mention any island, and the precise locality mentioned on both labels is in Amsterdam island; furthermore, collectors were on Amsterdam island on that date (15 Dec. 1963) as evidenced by other collection’s number right before and after collection’ number Lourteig 67. For these reasons, we definitely consider this mention ‘Kerguelen’ as an obvious label error, and Sagina hookeri Timaná, sp. nov. is not known to occur in Kerguelen.

ETYMOLOGY

Sagina hookeri Timaná, sp. nov. is named after the British botanist Sir Joseph Dalton Hooker (1817-1911), plant taxonomist, explorer and pioneer plant geographer. His monumental work “ The Botany of the Antarctic Voyage of H.M. discovery ships Erebus and Terror in the years 1839-1843 ” was a turning point in the study of the plant biogeography of the southern continents. He examined the flora of Île Amsterdam and Île Saint-Paul in his Flora Antarctica (Hooker 1844 -1847).

KEY TO THE SAGINA L. SPECIES PRESENT IN AMSTERDAM AND SAINT- PAUL ISLANDS

The following key, applicable to all known species of Sagina in Amsterdam and Saint-Paul Islands, is included here to help future field researchers working in the area.

1. Sepals appressed to capsule valves during capsular development, then diverging following dehiscence; pedicel recurved during capsular development.......................................................................... Sagina procumbens L.

— Sepals appressed to capsule valves during capsular development and during dehiscence; pedicel never recurved...................................................................................................................................................... 2

2 Plants caespitose, short, less than 3 cm tall (including inflorescence); flowers mostly tetramerous, rarely pentamerous; petal apex broadly ovate; capsule valve arching backwards at maturity........... Sagina hookeri Timaná, sp. nov.

— Plants diffuse, loosely spreading, 5–8 cm tall (including inflorescence); flowers tetramerous or pentamerous, even on the same individual; petal apex acute to obtuse; capsule valve erect at maturity...................................................................................................................................................... Sagina diffusa (Hook.f.) Timaná

DISTRIBUTION AND HABITAT

The species is endemic to Île Amsterdam and it is currently known from two distant places, in the north-west part near the cliff of La Pearl, and in the south-south-west part of the island, near Pointe Del Cano and crater Hébert including an area called ‘Terres Rouges’ (Fig. 1B) where it has been most often observed; this latter area is made of basalt-rich red soils along a unique narrow coastal strip of the island between Del Cano and Pointe Vlaming (Fig. 3E). Within the area, the species grows in hollows of ground in the middle of flat basalt rocks of lava flows.

Sagina hookeri Timaná, sp. nov. has never been observed in Île Amsterdam closely mixed with S. procumbens L., that was observed for the first time in 1985 in another station, i.e., Entrecasteaux (Jolinon 934 [P04937010!]).

CONSERVATION AND THREATS

Sagina hookeri Timaná, sp. nov. is rare on the island, or maybe overlooked: it is known from the type population near Del Cano extending from Terres Rouges to crater Hébert, and from an area of high cliffs. There is no known threat to the type locality in Del Cano, but the number of mature individuals (or cushionlike clumps) found here is estimated to be less than 250, thus the species is assessed as Endangered (EN) under criterion D (IUCN 2012). The population in cliffs of La Pearl might be threatened by likely landslide and crumbling substrate.

Given the Extend of Occurrence (EOO) and Area of Occupancy (AOO) estimated to 5.330 km 2, and 1.900 km 2 respectively (IUCN 2012), and the restricted size of the two known populations, inventories focused on these small flowering plants are needed in an effort to confirm the population size and its fluctuation. Any continuing decline observed or extreme fluctuation in the number of mature individuals could drive the species to become Critically Endangered in a very short time following criterion D of the IUCN Red List Categories and Criteria.

DISCUSSION

Although being geographic neighbors, Sagina hookeri Timaná, sp. nov. (Amsterdam Island) and S. diffusa (Hook.f.) Timaná (Saint-Paul Island) show clear morphological differences that justify recognition of the former as a distinct species. The most evident difference is habit: Sagina hookeri Timaná, sp. nov. produces a short, caespitose (cushion-like) growth form (Fig.3A), while the stems of S. diffusa are spreading, similar to S. procumbens L., with branches up to 8 cm long (Timaná 2018). In the case of S. hookeri Timaná, sp. nov. the entire plant size, including inflorescence, does not exceed 3 cm tall. The inflorescence of the new species described here is single-flowered, while in S. diffusa it tends to form a two-flowered cyme. Petals in S. hookeri Timaná, sp. nov. are wide obovate, much shorter than sepals, while those in S. diffusa are acute, rarely obtuse, and in some cases nearly as long as the sepals. In nature the capsule valve apex of the new species described here tends to arch backwards. Differences between S. hookeri Timaná, sp. nov. and S. procumbens include pedicel length, being less than 10 mm in the former and from 12 to 16 mm long in the latter; in addition branches in S. procumbens are filiform, less than 0.3 mm wide, and tangled, giving the plant a mat-like appearance (as in Cour 313 [P04970735!]). Sagina hookeri Timaná, sp. nov. individuals instead form robust, almost upright, discrete cushions (see Fig. 3A). Flower bud length is also quite different between these species: it is much smaller in S. procumbens (less than 2.5 mm long), while in Sagina hookeri Timaná, sp. nov. it can reach 3.5 mm long. Finally, the pedicel in S. procumbens is recurved during capsular development, at least in most cases.

While Sagina L. is a mostly northern hemisphere genus (Crow 1978), the new species here described adds to a group of species endemic to the southern hemisphere that has been reported in Chile (Marticorena & Quezada 1985), Australia (Adams 1996) and New Guinea (Larsen 1998).