Avicennia marina subsp. australasica Vierh.
Creators: name: Daniel, Thomas F.
Publisher: name: Zenodo
Year: 2016
Subjects: Biodiversity
Taxonomy
Plantae
Tracheophyta
Magnoliopsida
Lamiales
Acanthaceae
Avicennia
Avicennia marina

description: 3. Avicennia marina (Forsk.) Vierh., subsp. australasica (Walp.) J. Everett, Telopea 5(4): 628. 1994.
Avicennia tomentosa Sieber var. australasica Walp., Repert. Bot. Syst. 4: 133. 1845. Avicennia resinifera G. Forst., Pl. Esc. 72. 1786. Avicennia marina var. resinifera (G. Forst.) Bakh., Bull. Jard. Bot. Buitenzorg, ser. 3, 3: 210. 1921, nom illegit. (superfl.). TYPE.— Sheet 1460 in Thunberg’s herbarium (lectotype, designated by Everett [1994: 628]: UPS).
Figures 1H–K, 2, 3B,D
Shrubs to 2.3 m tall. Young stems of reproductive shoots covered with dense shiny granules or scalelike projections to 0.05 m long (scurfy), soon glabrate. Leaves petiolate, blades ovate to elliptic (to obovate), 44–100 mm long, 19–41 mm wide, 1.7–2.8 (–3.6) times longer than wide, acute (to rounded or emarginate) at apex, subattenuate to attenuate at base, surfaces discolorous (abaxial lighter), punctate-pitted (sometimes inconspicuously so abaxially), adaxial surface lacking trichomes, abaxial surface covered with a dense scurfy layer. Inflorescences of axillary and terminal (sessile to) pedunculate ± headlike spikes, peduncles (0–) 1–40 mm long, scurfy or distally pubescent like rachis, rachis not or but barely visible, internodes near midspike 1–4 mm long, scurfy and pubescent with ± antrorse eglandular trichomes to 0.2 mm long. Bracts opposite, broadly ovate to triangular, concavoconvex, 3–4 mm long, abaxial surface scurfy and often pubescent like rachis. Bracteoles similar to bracts except smaller. Flowers mostly 4–16 per spike, sessile. Calyx 3.5– 4 mm long, lobes elliptic to broadly elliptic, concavoconvex, imbricate, abaxially pubescent with antrorsely appressed eglandular trichomes to 0.8 mm long, margin ciliate with similar but spreading trichomes. Corollas 3.5–6. 5 mm long, internally drying dark or blackish proximally and light brownish distally (those from Australasia are usually described as yellowish or orangish and the color is often darker in the corolla tube), externally glabrous (tube and base of lobes) and densely pubescent with appressed eglandular trichomes to 0.2 mm long (remainder of lobes), tube 1.5– 2 mm long, limb actinomorphic, 4-lobed, lobes ovate-triangular to ovate-elliptic, 2–4. 5 mm long, apically entire (or 1 lobe sometimes slightly bifid apically with division to 0.2 mm long), internally lacking eglandular trichomes (at least distally) but sometimes punctate-pitted (proximally). Stamens 4, inserted in distal half of corolla tube near base of lobes, exserted from mouth of corolla tube, oriented symmetrically (i.e., equally distant from one another) around corolla with thecae opening toward central gynoecium, 1.5– 2 mm long, filaments 0.5– 0.8 mm long, anthers presented at same height, thecae 1– 1.2 mm long; pollen prolate spheroidal to euprolate, polar diameter (P) 28–41 µm, equatorial diameter (E) 24–27 µm, P: E = 1.04–1.75. Style not evident, stigma lobes 0.2 mm long. Fruit ovoid to subellipsoid, proximally blackish and distally light brownish when dry, 15–24 mm long, 10–19 mm across at widest expanse, pubescent with erect to flexuose to antrorse eglandular trichomes to 0.3 mm long (especially when less mature) and scurfy (especially evident when more mature). 2n = 64, 96 (Dawson 1989).
PHENOLOGY.— Flowering: February, August–September; fruiting: February, November.
DISTRIBUTION AND HABITAT.— Avicennia marina has the most extensive distribution among species in the genus; it is native to eastern Africa, southern Asia, Indian Ocean and western Pacific Ocean islands, and Australia. Subspecies australasica occurs primarily in subtropical and temperate Australasia (i.e., southeastern Australia and northern New Zealand). It is the southernmost-occurring taxon among species of Avicennia in the Old World (to 38°45’S; Duke 2006), and the southernmost-occurring mangrove in the world. In southern California, where this taxon has been introduced and become naturalized (Fig. 2), plants occur in salt marshes with Batis, Juamea, Salicornia, Spartina, and Suaeda at or near sea level.
ILLUSTRATIONS.— Munir (1986: 1179, fig. 546); Duke (1991: 314, fig. 7); Clarke and Myerscough (1991: 285, fig. 1).
NOMENCLATURE.— The name “ A. marina var. australasica (Walp.) Moldenke ” has been used for this taxon, but as discussed by Everett (1994), this combination was not validly published at this rank, and other infraspecific taxa of A. marina are currently treated as subspecies. Avicennia marina subsp. australasica and the synonyms noted above are all based on A. resinifera. See Moldenke (1960) and Duke (1991) for a full list of synonyms of Avicennia marina.
LOCAL NAME.— Gray mangrove.
CONSERVATION.— Avicennia marina has been assessed as a taxon of Least Concern (LC) by Duke et al. (2010). This taxon is not native in the New World, but has become naturalized locally and is potentially invasive. On his collection 28024 made in 1979, Moran noted that plants in California had been introduced from Aukland, New Zealand about 1966–69. He also noted the presence of about 100 or more flowering-size plants plus many seedlings in the wildlife reserve where his observations were made. Initial efforts to eradicate the species were unsuccessful.
DISCUSSION.— This species is readily distinguished from those native to the western Hemisphere by its actinomorphic flowers with yellowish to orangish corollas bearing ovate-triangular to ovate-elliptic lobes and its equidistant stamens that are inserted near the base of the corolla lobes, dehisce toward the center of the flower, and vary from 1.5– 2 mm in length (Fig. 3B).
Duke et al. (1998) provided genetic evidence that supported the morphological recognition of A. marina as a distinct species and that supported recognition of the three infraspecific taxa (treated by him as varieties, but here recognized as subspecies): subsp. marina, subsp. eucalyptifolia (Valeton) J. Everett, and subsp. australasica. The latter subspecies would appear to consist of or contain polyploids based on the reported chromosome numbers of 2n = 64 and 96 (Dawson 1989, as A. resinifera). These numbers suggest a possible base number of x = 8 or x = 16. A chromosome number of 2n = 36 was reported for an unspecified subspecies of A. marina by Subramanian (1988; without citation of voucher). These appear to be the only recent chromosome counts for both this species and for the genus. If these numbers are accurate, both polyploidy and dysploidy would appear to have played a role in the evolution of taxa in A. marina. The only other known chromosome counts for Avicennia are 2n = ca. 66 and n = ca. 33 by Raghavan and Arora (1958; with a meiotic figure showing n = 33, but without citation of a voucher) for A. alba Bl. Sanders (1997) indicated a base chromosome number for Avicenniaceae of x = 18. Although no rationale was stated for this number, his conclusion was probably based largely on Subramanian’s count of 2n = 36 for A. marina.
Avicennia marina subsp. australasica was distinguished by Duke (1991) from the other two varieties of A. marina by the fully (or nearly so) pubescent calyces (vs. pubescent only near the base), and the gray, fissured (vs. green, chalky smooth, and often flaky in patches) bark of the mature trunk.
SPECIMENS EXAMINED.— U.S.A. California: San Diego Co.: Northern Wildlife Preserve, North Mission Bay, tidal area 100 m W of Rose Creek, 32.7949°N, 117.2247°W, I. Kay 29 (UCR); E edge of Kendall / Frost Marsh, Mission Bay, San Diego, ca. 32˚47.5ʹN, 117˚13.8ʹW, sea level, 9 September 1979, R. Moran 28024 (CAS, GH, MEXU, NY, UC, US); same locality, 12 June 1990, R. Moran 31036 (CAS, JEPS).
description: Published as part of Daniel, Thomas F., 2016, Avicennia (Acanthaceae: Avicennioideae) in North America and Mesoamerica, pp. 163-189 in Proceedings of the California Academy of Sciences 63 (5) on pages 184-186, DOI: 10.5281/zenodo.11512418