Laurencia, J. V. Lamouroux, 1813

Metti, Yola, Furnari, Giovanni & Serio, Donatella, 2024, Molecular analyses reveal the presence of Corynecladia J. Agardh (Rhodophyta, Rhodomelaceae) in the Mediterranean Sea with two new species, C. millarii sp. nov. and C. mediterranea sp. nov., Cryptogamie, Algologie 20 (2), pp. 11-30 : 20-21

KEY TO THE MEDITERRANEAN SPECIES OF THE LaUReNcIa COMPLEX

1. Thalli throughout compressed or with only ultimate branchlets cylindrical. Two pericentral cells per axial segment, spermatangial branches of filament-type and tetasporangia produced from epidermal cells ................ 2

— Thalli throughout cylindrical. Two or four pericentral cells per axial segment .............................................. 6

2. Secondary pit connections between epidermal cells present ......................................................................... 3

— Secondary pit connections between epidermal cells absent .......................................................................... 5

3. Axes arising from a spreading basal crust. Spermatangial depressions cup-like, but slightly sunken. Species living in the littoral zone .......................................................................................... Osmundea verlaquei G.Furnari

— Axe(s) arising from a discoid holdfast or from a stoloniferous holdfast ......................................................... 4

4. Epidermal cells in surface view very elongated longitudinally. Spermatangial depressions cup-shaped. Cystocarps urceolate. Species living in the lower littoral zone to upper sublittoral zone ..................................................... ......................................................................................... Osmundea truncata (Kützing) K.W.Nam & Maggs

— Epidermal cells in surface view very elongated longitudinally in the basal and median parts of the thallus, isodiametric in the subapical parts. Spermatangial depressions cup-shaped, but slightly sunken, located at the bifurcation of the branches. Cystocarps ovoid. Species living in the upper sublittoral zone (up to 7 m depth) ......................................................................................................... Osmundea oederi (Gunnerus) G.Furnari

— Epidermal cells in surface view polyhedral. Spermatangial depressions pocket-shaped. Cystocarps ovoid. Species living in the lower sublittoral zone or if in shallower water in shaded habitats ................................................. ...................................................................................................... Osmundea pelagosae (Schiffner) K.W.Nam

5. Axes arising from a thick spreading crust. Epidermal cells, in transverse section, radially elongated and palisade-like. Medullary cells without lenticular thickenings. Spermatangial depressions cup-shaped. Species living in the littoral zone ................................................................................................... Osmundea pelagiensis G.Furnari

— Axes arising from a stoloniferous holdfast. Epidermal cells, in transverse section, obconic and not palsade-like. Medullary cells with lenticular thickenings. Spermatangial depressions pocket-shaped. Species living in the littoral zone ................................................................................... Osmundea pinnatifida (Hudson) Stackhouse (Its occurrence in the Mediterranean sea should be confirmed.)

6. Secondary pit connections between epidermal cells present. Four pericentral cells per axial segment ........... 7

— Secondary pit connections between epidermal cells absent. Two pericentral cells per axial segment ........... 16

7. Adult thalli not taller than 20 mm .............................................................................................................. 8

— Thalli up to 15 cm or more high ................................................................................................................. 9

8. One to three (rarely four) erect axes, arising from a discoid holdfast. Axes simple or with one short subapical branchlet. Epidermal cells slightly projecting near the apex. Medullary cells with lenticular thickenings. Species epiphytic on both seagrasses leaves and macroalgae ......................................................................................... ....................... Laurencia minuta Vandermeulen, Garbary & Guiry subsp. scammaccae G.Furnari & Cormaci

— One (occasionally two or three) erect axes arising from a discoid holdfast. Axes to four orders of ramification. Epidermal cells not projecting near the apex. Species epiphytic only on seagrasses leaves................................. ................................................................................................................. Laurencia epiphylla Boisset & Lino

9. Thalli more or less densely entangled ......................................................................................................... 10

— Thalli erect not entangled .......................................................................................................................... 11

10. Thalli densely entangled forming compact tufts. Branching irregularly spiral. In transverse section the axial cell not distinguishable in median portions of the thallus. Species living in the lower littoral to upper sublittoral zones ........................................................................................................ Laurencia intricata J.V.Lamouroux

— Thalli prostrate flexuous and frequently entangled. In transverse section, the axial cell is readily distinguishable in median portions of the thallus. Branching sparse, irregular with branches and branchlets often inserted nearly at a right angle. Branchlets with apices obtuse. Species living in the lower sublittoral zone or if in shallower water in shaded habitats ......................................................................................... Laurencia chondrioides BØrgesen

11. Presence of deciduous branchlets formed abundantly near branches. Species living in the sublittoral zone ............................................................................................ Laurencia caduciramulosa Masuda & Kawaguchi

— Absence of deciduous branchlets ............................................................................................................... 12

12. Axes radially ramified. Branches and branchlets spirally ramified giving a pyramidal outline to the thallus ... 13

— Axes irregularly or whorled ramified .......................................................................................................... 14

13. Thalli soft in texture. Axes not percurrent. Epidermal cells very projecting near the apex. Tetrasporangia produced from both the third and the fourth pericentral cells. Species living in the lower littoral to upper sublittoral zone ............................................................. Laurenciella marilzae (Gil-Rodríguez et al.) Gil-Rodríguez et al.

— Thalli more or less cartilagineous in texture. Axes percurrent, branchlets often grouped in whorls, decreasing in lenght in the upper parts of the thallus giving it a conical outline. Epidermal cells not projecting near the apex. Tetrasporangia produced from only the fourth pericentral cell. Species living in the sublittoral zone ........................................................................................................... Laurencia pyramidalis Bory ex Kützing

14. In surface view, secondary pit-connections easily visible. In longitudinal section they appear localized in the outer part of the cells ................................................................................................................................. 15

— In surface view, secondary pit-connections thin and hardly visible. In longitudinal section they appear localized in the middle to inner part of the cells. Species living in the lower littoral to upper subittoral zone ................ ................................................................................. Corynecladia millarii Metti, G.Furnari & Serio , sp. nov.

— ....................................................................... Corynecladia mediterranea Metti, G. Furnari & Serio , sp. nov. (The above two species distinguish each other only in different molecular sequences.)

15. Branches and branchlets irregularly ramified. Medullary cells without lenticular thickenings. Species living in the sublittoral zone ...................................................................... Laurencia obtusa (Hudson) J.V.Lamouroux

— Branches and branchlets in whorls of 2-3, clavate and restricted at their bases. Medullary cells with lenticular thickenings. Species living in the sublittoral zone ............................................ Laurencia microcladia Kützing

— Branches and branchlets very short with wart-like ultimate branchlets subverticillately arranged. Medullary cells without lenticular thickenings. Species living in the lower littoral to upper sublittoral zones ........................................................................................................ Laurencia glandulifera (Kützing) Kützing

16. Thalli soft in texture. Spermatangial branches of filament-type and tetasporangia produced from epidermal cells. Species living in the lower littoral zone ............................. Osmundea maggsiana Serio, Cormaci & G.Furnari

— Thalli cartilaginous in texture. Spermatangial branches of trichoblast-type, tetrasporangia produced from pericentral cells ................................................................................................................................................ 17

17. Axes arising from a thick basal crust. Thalli yellowish, blackish at the base. Species living in the littoral zone .............................................................. Palisada tenerrima (Cremades) Serio, Cormaci, G.Furnari & Boisset

— Axes arising from a discoid holdfast with or without stolon-like branches ................................................. 18

18. Epidermal cells of branches and all ultimate branchlets in transverse section obconic and not palisade-like. Branching divaricate with branches arising at open angles to 90°. Species living in the littoral zone in bays and lagoon ................................................................................. Palisada patentiramea (Montagne) Cassano et al.

— Epidermal cells of branches and ultimate branchlets in transverse section radially elongated and palisade-like .................................................................................................................................................................. 19

19. Axes and branches irregularly and alternately ramified. Apices sunken with mamillate edges. Species living in the sublittoral zone ........................................................................ Palisada thuyoides (Kützing) Cassano et al.

— Axes and branches very densely clothed with numerous truncate, wart-like ultimate branchlets, subverticillately arranged. Species living in the lower littoral zone ..................................... Palisada perforata (Bory) K.W.Nam

— Axes irregularly ramified, naked in the proximal parts. Branches irregularly and alternately ramified, branchlets subopposite, frequently subverticillately arranged in the median parts, branches of the third order often unilateral. Species living in the upper sublittoral zone ............. Palisada maris-rubri (K.W.Nam & Saito) K.W.Nam