Limonium steppicum Sefi, Ghrabi-Gammar & Brullo, 2020

Sefi, Ons, Ghrabi-Gammar, Zeineb, Jilani, Imtinen Ben Haj, Daoud-Bouattour, Amina & Brullo, Salvatore, 2020, A new species of Limonium from Tunisia, Phytotaxa 446 (5), pp. 281-290 : 281-289

Limonium steppicum Sefi, Ghrabi-Gammar & Brullo sp.nov. ( Fig. 1 ).

A Limonio rubescentis foliis 3–5 nervis, evidenter mucronatis, scapo max. 60 cm alto, ramulis inflorescentiae paucis, spicis brevioribus, densis, spiculis 4,5– 5 mm longis, 5–8 floris, ad 9–10 in 1 cm dispositis, bractea inferiori 1,8– 2 mm longa, ovata, bractea media rotundata, bractea interiori 3–3,5 mm longa, ovata, acumine 0,8– 1 mm longo, calyce 3,1–3,4 mm longo, tubo sparsim puberulo, lobis ovatis, 0,5–0,6 mm longis, costis superantibus basi loborum differt.

Type:— TUNISIA. Djerba, sur la route entre Ghardaia et El Kantara, 13 September 2019, Ons Sefi s.n. (holotype CAT!, isotypes CAT!, INAT!).

Perennial, glabrous, with short caudicles. Leaves evergreen, rigid, rosulate, densely inserted on the caudicles, glaucous, lanceolate to oblanceolate, (1)–3–5 (7)-nerved, 2–10 cm long, 6–22 mm wide, with narrow cartilagineous margin, mucronate, with mucro 1–3 mm long, acute to subobtuse at the apex. Stem usually solitary, 40–60 cm long, erect, long naked below, branched above, without steriles branches. Inflorescence paniculate, with branches rigid and divaricate. Spikes 5–22 mm long, divaricated, distichous, densely arranged. Spikelets 4.5–5 mm long, 9–10 per cm, 5–8 flowered. Outer bract 1.8–2 mm long, ovate, acute, coriaceous in the central part, forming point 1.2–1.4 mm long, membranous at margin. Middle bract membranous, rounded, 1.4–1.6 mm long. Inner bract 3–3.5 mm long, 2.8–3 mm wide, ovate, obtuse, with outer hyaline margin and pale brown inner margin, central part herbaceous, with a point 0.8–1.0 mm long, not reaching the apex. Calyx 3.1–3.4 mm long, sparsely hairy in the tube, 0.5–1 mm protruding from the inner bract, with limb slightly longer than the tube, lobes ovate 0.5–0.6 mm long, with midribs exceeding the base of the lobes.

Habitat and Distribution:— Limonium steppicum is localized in a small area south of the island of Djerba, between El Kantara and the nearby continental coast in the territory of Zarzis, which are connected by an ancient Roman road built on the sea, which in that stretch is shallow ( Fig. 2 ). Concerning its ecological requirements, it is a halophyte linked to very dry soil, mainly during the spring-summer period, constituted by debris of fine and coarse sands rich in chlorides. This species is usually a member of a perennial plant community characterized by Aeluropus lagopoides ( Linnaeus 1767: 33) Trin. ex Thwaites (1864: 374) , Frankenia thymifolia Desfontaines (1798: 316) , Nitraria retusa (Forsskal, 1775: 221) Ascherson (1876: 94) , Limonium alleizettei ( Pau 1929: 92) Brullo & Erben (1989: 493) , L. rubescens Brullo & Erben (1989: 459) , Zygophyllum album Linnaeus. fil. (1762: 11), etc.

Etymology:—The epithet “ steppicum ” is in reference to the habitat where the plant grows.

Phenology:—Flowering from June to September.

Taxonomic remarks:—For its habit and some morphological features, such as rosulate, glaucous and rigid leaves, stem without sterile branches and small spikelets, Limonium steppicum shows very close relationships mainly with L. rubescens , which according to Brullo & Erben (1989) is distributed in the salt marshes of southern Tunisia and occurs also in Djerba, where it is quite frequent ( Fig. 3 ). However, L. rubescens differs from L. steppicum in having leaves 5–7 nerved, not manifestly mucronate at the apex, stem usually non solitary, up to 80 cm tall, inflorescence very branched and broad, spikes more lax, 15–55 mm long, spikelets 5–6 mm long, (1–) 3–5 flowered, 4–6 per cm arranged, outer bract 2–2.8 mm long, triangular-ovate, middle bract ovate to elliptical, inner bract 3.8–4.6 mm long, elliptical, with a point 0.9–1.3 mm long, calyx 3.8–4.2 mm long, with tube pubescent, lobes triangular-ovate, 0.4 mm long, with midribs not exceeding the base of the lobes ( Fig. 4 ). The two species are well differentiated also from the ecological viewpoint, since L. rubescens grows in surfaces periodically submerged by brackish waters, with soils richer in sandy component and quite damp in the summer, while L. steppicum shows more xeric requirements being linked to stands not subject to submersion, with very dry salt soils rich in coarse material, as the outer and raised edges of the coastal salt marshes usually more far from the shoreline. Previously, from Djerba other Limonium species were described by Brullo & Erben (1989) and Bartolo et al. (2003), such as L. byzacium Brullo & Erben (1989: 419) , L. meningense Brullo & Erben (1989:447) and L. formosum Bartolo, Brullo & Giusso (2003: 537) , which are morphologically well differentiated from L. steppicum and L. rubescens , as well as for their ecological requirements. As shown in Table 1 the aforesaid species are distinguished by several diacritical features concerning the habit, leaves, inflorescence, spike and spikelets. The main diagnostic morphological characters that allow to differentiate these species are emphasized in the following analytical key:

The key regarding Limonium steppicum and allied species occurring in Djerba

1. Inner bract 4.5–5 mm long, calyx 4–4.8 mm long, calyx lobes semi-elliptical to semi-circular .......................................................2

- Inner bract 3–4.6 mm long, calyx 2.9–4.2 mm long, calyx lobes ovate to triangular-ovate..............................................................3

2. Stem 20–30 cm height, with 1–3 internodes, leaf 2–6 cm long, with 1–3(5) nerves, inflorescence branched in the lower part of the stem, with branches 2–3.5 cm long, middle bract 2.5–2.8 mm long, inner bract rounded at apex, with midrib not reaching the apex.................................................................................................................................................................................. L. formosum

- Stem 50–80 cm height, with 6–7 internodes, leaf 5–14 cm long, with 5–7 nerves, inflorescence branched in the upper half of the stem, with branches up to 30 cm long, middle bract 2–2.1 mm long, inner bract acuminate at apex, with midrib reaching almost the apex.................................................................................................................................................................................. L. menigense

3. Stem with 5–6 internodes, leaf with (1)3–5 nerves, inflorescence branched in the upper half of the stem, with branches 1.5–6 cm long, spikelet 9–10 per cm, outer bract ovate, with midrib reaching the apex, inner bract ovate, calyx lobes ovate, with midrib exceeding the base........................................................................................................................................................... L. steppicum

- Stem with 2–4(5) internodes, leaf with 5–9 nerves, inflorescence branched in the lower half of the stem, with branches up to 22–30 cm long, spikelet 4–8 per cm, outer bract triangular-ovate, with midrib not reaching the apex, inner bract elliptical, calyx lobes triangular-ovate, with midrib not reaching or reaching the base........................................................................................................4

4. Stem internodes 4–12 cm long, leaves lanceolate to oblanceolate, 7–20(30) mm wide, with mucro not evident or rarely 0.5 mm long, inflorescence laxly branched, with spikes 15–55 mm long, spikelets unilateral laxly arranged, 4–6 per cm, 4–6 mm long, outer bract 2–2.8 mm long, inner bract 3.8–4.6 mm long, calyx 3.8–4.2 mm long, with tube densely pubescent......... L. rubescens

- Stem internodes 2–5 cm long, leaves spathulate to oblanceolate-spathulate, 20–55 mm wide, with mucro 2 mm long, inflorescence densely and very branched, with spikes 7–15 mm long, spikelets disitichous densely arranged, 7-8 per cm, 4–4.5 mm long, outer bract 1.2–1.6 mm long, inner bract 3–3.4 mm long, calyx 2.9–3.4(3.8) mm long, with tube unilaterally hairy ............. L. byzacium

Other specimens examined of Limonium steppicum (paratypes):— TUNISIA. Djerba , Ghardaia, 13 September 2019, Ons Sefi s.n. ( CAT!) ; Djerba , sur la route Romaine au Sud de El Kantara, 13 September 2019, Ons Sefi s.n. ( CAT!) ; Jurf Al Kantara , 13 September 2019, Ons Sefi s.n. ( CAT!) .

Specimens examined of Limonium rubescens :— TUNISIA. Between Sfax and Gafsa, c. 15 km NE of the village of Mezzouna along the road P1 ; salty sandy places, 4 September 1984, Brullo & Erben 665, (holotype M!, Isotype CAT!) ; Djerba, près de l’Aéroport, 1 May 2019, O. Sefi, Z. Ghrabi-Gammar, A. Daoud-Bouattour , I. Ben Haj Jilani s.n. ( CAT!) ; Djerba, près de l’Hôtel Dar Jerba, 30 April 2019, O. Sefi, Z. Ghrabi-Gammar, A. Daoud-Bouattour , I. Ben Haj Jilani s.n. ( CAT!) ; Djerba, Sidi Yati, 13 September 2019, Ons Sefi s.n. ( CAT!) ; Djerba, Sidi Yati, 30 April 2019, O. Sefi, Z. Ghrabi-Gammar, A. Daoud-Bouattour , I. Ben Haj Jilani s.n. ( CAT!) ; Tataouine, Oued Tlelet, 28 April 2018, Ons Sefi s.n. ( CAT!) ; Jurf Al Kantara près de Zarzis, 26 April 2018, Ons Sefi s.n. ( CAT!) ; Djerba, Ajim, 1 May 2019, O. Sefi, Z. Ghrabi-Gammar, A. Daoud-Bouattour , I. Ben Haj Jilani s.n. ( CAT!) .

Figures

FIGURE 1. Diagnostic features of Limonium steppicum. A. Habit. B. Inflorescence. C. Spikelet. D. Inner bract, lateral view. E. Inner bracts, dorsal view. F. Calyces. G. Outer bracts. H. Middle bracts. I. Leaves. L. Calyx lobes. Illustration by S. Brullo based on living material coming from the type locality (CAT).

FIGURE 2. Geographical distribution of Limonium steppicum (red dot), in Tunisia.

FIGURE 3. Geographical distribution of Limonium rubescens (blue dot), in Tunisia from Brullo & Erben (1989).

FIGURE 4. Diagnostic features of Limonium rubescens. A. Habit. B. Inflorescence. C. Spikelet. D. Inner bract, lateral view. E. Inner bract, dorsal view. F. Calyx. G. Outer bract. H. Middle bract. I. Leaves. L. Calyx lobes. Illustration by S. Brullo based on living material coming from Djerba, Sidi Yati, 13 September 2019, Ons Sefi s.n. (CAT).