Laurencia karachiana Bibi, Cassano & Rasheed 2019, sp. nov.
Creators: name: Bibi, Rabia
name: Cassano, Valéria
name: Medeiros, Rosângela Da Silva
name: Rashid, Shahnaz
name: Rasheed, Munawwer
Publisher: name: Zenodo
Year: 2019
Subjects: Biodiversity
Taxonomy
Plantae
Rhodophyta
Florideophyceae
Ceramiales
Rhodomelaceae
Laurencia
Laurencia karachiana

description: Laurencia karachiana Bibi, Cassano & Rasheed sp. nov. (Fig. 4A–G, Fig. 5A–G, Fig. 6A–F, Fig. 7 A–F).
Type locality:— PAKISTAN. Karachi: French Beach (Buleji), male specimen, 24 o 50ꞌ15ꞌꞌN, 66 o 49ꞌ11ꞌꞌE, 13 August 2018, coll. R. Bibi (holotype KUH-SW-1312) deposited in the Karachi University Herbarium). GenBank accession number for rbc L (MK 796228) and for COI-5 P (MK 796229). Isotype: SPF 58339, female, male and tetrasporangial plants.
Etymology:—The specific epithet refers to the Karachi coast, where the plants were collected.
Description:— Habit: Plants erect forming tufts 5–12 cm high (Fig. 4 A-C), pinkish-red, purple or reddish-brown in colour, sometimes greenish in the main axes and primary lateral branches and pinkish-red in remaining portions of the plant. Thalli are terete, cartilaginous in texture, attached to the substratum by a discoid holdfast (Fig. 4D), basal descending branches, and stoloniferous branches with several smaller holdfasts providing secondary and stronger attachment to the substratum. Main axes 1225–1375 μm in diameter in the middle portion of the thallus. Erect axes irregularly alternate and spirally arranged, uniformly dense in the mid-upper portions of the thallus with up to 4 (5) orders of branches, and sometimes scant or naked in the lower portions (Fig. 4C). Lateral branches display the same branching pattern as the main axes, becoming increasingly shorter upwards, resulting in a thallus with a pyramidal outline (Fig. 4 A-C). Numerous ultimate branchlets are cylindrical to clavate with truncated tips, 575 (775–2800) 3300 μm long and 325–625 μm in diameter.
Vegetative structures: In surface view, cortical cells have one corp en cerise per cell (Fig. 4E), with one per trichoblast cell. Cortical cells are arranged regularly in longitudinal rows and connected to each other by longitudinally oriented secondary pit-connections (Fig. 4F). Cortical cells are rounded to polygonal at basal and apical portions of the thallus, and slightly polygonal and longitudinally elongated in middle portions of main axes, 90–225 x 52.5–80 μm. In median longitudinal sections through a branchlet, the outer cortical cell walls near the apices do not project beyond the surface. In transverse section, the thallus has 1–2 layers of pigmented cortical cells and 4–5 layers of hyaline medullary cells (Fig. 4G). Cortical cells are quadrate, cuneiform to rectangular, not arranged as a palisade, and 22.5–52.5 x 20–45 μm in the middle portions of thalli. Medullary cells are rounded to slightly radially elongated, and 62.5–107.5 x 35–110 μm, gradually increasing in size toward the center of the thallus. Each vegetative axial segment cuts off four pericentral cells slightly larger than the other surrounding cells (Fig. 5A). Lenticular thickenings rare, occurring in the walls of the medullary cells of the lateral branches only observed in female plants (Fig. 5B). At branch apices, the first pericentral cell is produced beneath the basal cell of the trichoblast.
Reproductive structures: Male plants with clavate branches, characteristically swollen and compound-cymose, measuring 800 (1000–1800) 2000 μm in diameter (Fig. 4A, Fig. 5C, D). In longitudinal section through a fertile branchlet, the spermatangial pits are cup-shaped, and an axial cell row is discernible at the base (Fig. 5E). Spermatangial trichoblasts arise from the axial cell, and consist of fertile and sterile branches (Fig. 5F); the fertile branches produce many ovoid spermatangia measuring 7.5–10 x 5–7.5 μm, and terminate in vesicular sterile cells, of 17.5–22.5 x 12.5– 17.5 μm; each spermatium possesses an apical nucleus (Fig. 5G).
Female plants (Fig. 4B, Fig. 6A, B) with procarp developed from the basal cell of the trichoblast near the apical cell of the branchlet. Procarp with five pericentral cells, the fifth becoming the supporting cell of a four-celled carpogonial branch, with two groups of sterile cells (basal and lateral) (Fig. 6 D-F). Gonimoblast filaments forming numerous terminal, clavate shaped carposporangia, 122.5–182.5 x 32.5–87.5 μm. Cystocarps conical with 150–177.5 μm in diameter and prominent in the thallus, arranged subapically in the branchlets, without protuberant ostioles (Fig. 6 AC).
Tetrasporangial branchlets are cylindrical, simple or compound, (475) 900–2800 (4600) x 300–525 μm (Fig. 7A, B). At the apex of the branchlets, each axial segment produced two pericentral cells fertile, the third and fourth, and the other two pericentral cells remained vegetative (Fig. 7C). Each fertile pericentral cell cut off distally two pre-sporangial cover cells, abaxially the tetrasporangial mother cell, and subsequently, one post-sporangial cover cell (Fig. 7D, E). The post-sporangial cell divided and contributed to the formation of the cortication around the tetrasporangium. The pre-sporangial cells do not divide and have no secondary pit-connections. Tetrasporangia maturation occurs in a clockwise spiral, as new tetrasporangia are produced in a parallel pattern in relation to the fertile axis (Fig. 7F). Tetrasporangia are tetraherally divided and 112.5–147.7 μm in diameter.
Material examined: — PAKISTAN. Karachi: French Beach (Buleji), intertidal, epilithic, 03 September 2014, R. Bibi (KUH-SW-No. 1341-i), 06 August 2015, R. Bibi (KUH-SW-No. 1341-ii), 23 September 2016, R. Bibi (KUH-SWNo.724-ii), 11 September 2018, R. Bibi (KUH-SW-No.134-iii); intertidal rock pools, epilithic, 05 November 2014, R. Bibi (KUH-SW-No.1310b).
Distribution and habitat: —This species is currently known only from the Indian Ocean: Karachi, Pakistan. Epilithic specimens of Laurencia karachiana were found on the rocky shore, growing in rocky pools in shallow water in the mid- and lower intertidal zones, in protected to moderately exposed wave exposures. Also found epiphytically on the drifted seaweeds, such as Sargassum sp.
description: Published as part of Bibi, Rabia, Cassano, Valéria, Medeiros, Rosângela Da Silva, Rashid, Shahnaz & Rasheed, Munawwer, 2019, Morphological and molecular systematic investigation of Laurencia karachiana sp. nov. (Ceramiales, Rhodophyta) from Karachi, Pakistan, pp. 23-40 in Phytotaxa 404 (1) on pages 28-30, DOI: 10.11646/phytotaxa.404.1.3, http://zenodo.org/record/13715961