Dichotomaria marginata (J. Ellis et Solander) Lamarck 1816 , p. 146

Schneider, Craig W., Popolizio, Thea R., Spagnuolo, Dylan S. & Lane, Christopher E., 2016, Notes on the marine algae of the Bermudas. 15. Dichotomaria huismanii (Galaxauraceae, Rhodophyta), a new species in the D. marginata complex from the western Atlantic, Botanica Marina (Warsaw, Poland) 59 (1), pp. 13-29 : 17-23

Dichotomaria marginata (J. Ellis et Solander) Lamarck 1816, p. 146 ( Figures 3–6 )

Basionym

Corallina marginata J. Ellis et Solander 1786, p. 115 , pl. 22 figure 6 ( Figure 3 ).

Description

Rosy-brown plants to 10 cm tall and 13 cm across, composed of dichotomously branched flattened axes with thickened margins, these showing faint annulations; axes mottled in appearance when dried; internodes 4.7–13.7 mm long and 1.6–2.6 mm wide; axes branching dichotomously at angles of 72–89°; cortex of sporophytes composed of two layers of cells, outer cortical assimilatory cells subspherical to ovoid, 20–40 µm long and (21–) 33–49 µm diameter, and an inner layer of flared stalk cells each bearing 1–2 assimilatory cells, 15–36 µm long and 5–10 µm diameter (at narrowest point); stalk cells borne typically in pairs though occasionally singly on the outer surface of the inner cortex; stalk cells most commonly unicellular, rarely two-celled; inner cortex consisting of typically one, occasionally two, layers of transversely ovoid to rectangular cells, 50–115 µm diameter and 25–68 µm high; subcortical cells subspherical at margins; medullary filaments extending from subcortical cells, 7–13 µm diameter; gametangia and tetrasporangia not seen in our sequenced specimens.

Type locality

“… on the shore of one of the Bahama islands”, West Indies, western Atlantic Ocean ( Ellis and Solander 1786).

Distribution

Formerly reported as pantropical, genetically verified specimens are known from Guadeloupe, Puerto Rico and St. Croix, USVI (West Indies).

Selected collections

St. Croix, Virgin Is. – T. R. Popolizio ( TRP)/ C. E. Lane ( CEL)/ E.D. Salomaki ( EDS) 13-24-1 [ STX 032] ( Figure 4 ), TRP / CEL / EDS 13-25-9 [ STX 054] (see Table 1 for collection details).

Remarks

As discussed above, two St. Croix collections genetically matched other sequenced specimens from Guadeloupe and Puerto Rico, as well as the description of Dichotomaria marginata provided by Papenfuss et al. (1982). This has allowed us to identify STX 032 and STX 054 ( Figures 1 and 2 ) as true representatives of D. marginata in the West Indies, a species with a type locality in the Bahamas ( Silva et al. 1996). All of the genetic collections made in St. Croix identified as D. marginata have the anatomy of sporophytes defined for the species, unfortunately none bearing tetrasporangia. Thus, we cannot provide tetrasporangial size and shape nor the anatomy or reproduction in gametophytes of these genetically significant D. marginata vouchers. Although there are reports about these features in earlier literature (e.g. BØrgesen 1916, Howe 1918b, Taylor 1960, Papenfuss et al. 1982), without a molecular tie to this species where crypsis is now reported, we are hesitant to link that information here.

Similar to what Huisman et al. (2004) found for the species, tetrasporic St. Croix representatives of D. marginata have “the presence of a distinctly thickened margin (particularly noticeable when dried)” and a “cortex of the tetrasporophyte bearing paired subspherical cells (at least some with a small terminal spine)” ( Figure 5 ). As was pointed out in the Ellis and Solander (1786) protologue, the flattened axes of D. marginata are more pronounced when removed from the water, the first collections being washed up and dried on a Bahamian beach. Our specimens have three, or occasionally four, layers of cells including stalk and outer assimilatory cells. The assimilatory cells of St. Croix D. marginata are subspherical to ovoid in cross-section ( Figure 5 ), and appear circular to ellipsoidal in surface view ( Figure 6 ). Some, but not a majority, of the assimilatory cells are apiculate, these cells usually paired on stalk cells that are mostly paired on outer subcortical cells ( Figure 5 ). The subcortical cells are transversely ovoid to rectangular, and occasionally subspherical at the margins ( Figure 5 ).

Howe (1918b) was the first to consider Galaxaura occidentalis BØrgesen (type locality= Virgin Islands) as the gametophyte generation of G. marginata , and BØrgesen (1920) and subsequent workers ( Taylor 1960, Papenfuss et al. 1982) followed his supposition. Howe (1918a) mentioned gametophytic specimens in his account of G. marginata in the Bermuda flora, but it remains unclear whether he was referring to actual Bermuda gametophytes or rather to the gametophytes he was working on at the same time from the West Indies ( Howe 1918b). We have been able to observe the gametophytic holotype of G. occidentalis [in C], most reasonably the alternate generation of the sporangial D. marginata , but this requires genetic confirmation. It would be helpful to find sporophytes and gametophytes of D. marginata in a single Bahamian or West Indian population to confirm this supposition, both generations matching genetic sequences already linked to this species from the West Indies.

A second genetic species, Dichotomaria sp. 1 CRB, was collected in St. Croix and St. Kitts ( Figures 1 and 2 , Tables 1 and 2 ), and the St. Croix isolate represents the gametophytic stage of an undescribed species in the D. marginata complex. The St. Croix specimen has anatomical similarities with the type of G. occidentalis ; unfortunately, it is genetically distinct from local and regional D. marginata . We only have two representatives of this species from the West Indies, thus until additional specimens are obtained and sequenced, Dichotomaria sp. 1 CRB will remain undescribed. Whether its gametophytic stage represents what was described as G. occidentalis requires further investigation. Nevertheless, its sequence demonstrates that there are at least two species in the D. marginata complex in the West Indies.

Figures

Figure 1: Species groups in the Galaxauraceae determined with UPGMA clustering of the COI-5P genetic barcode, with Scinaia and Liagora as outgroups. Sequences generated for this study are in bold text.

Figure 2: Phylogeny of the Galaxauraceae based on maximum-likelihood analyses of rbcL sequences. Branch values are bootstrap supports for ML (1000 replicates) followed by Bayesian posterior probabilities expressed as a percentage of support out of 1. An asterisk (*) indicates 100% support for both robustness metrics while a dash (-) indicates support values <60%. Sequences generated for this study are in bold text.

Figures 3–6: Dichotomaria marginata. (3) Lectotype of Corallina marginata (=Dichotomaria marginata): Ellis and Solander illustration (1786, pl. 22 figure 6). (4) Sample from St. Croix (STX032), scale bar=2 cm. (5) Section through outer cortex showing subcortical cell bearing a pair of assimilatory outer cortical cells, scale bar=25 µm. (6) Surface view of outer cortical assimilatory cells (STX054), scale bar=25 µm.

Tables

Table 1: Collection details for isolates included in the molecular analyses of this study with newly generated GenBank accession numbers in bold type.

Species	Voucher nos.	Collectors/date	Collection site	COI-5 P	rbc L
Galaxauraceae Actinotrichia fragilis (Forsskål) BØrgesen	GWS 000151	J. Huisman/ 17 Aug. 1995	Ningaloo Reef, Western Australia, Australia	KT886155
	–	T. Schils, K. Pauly and E. Demeulenaere/ 28 Oct. 2004	Bandar Khayran, Capital Area, Oman		EU 095253
	CNU 32154	20 Jan. 2006	Bonbon, Cagayan de Oro, Philippines	KC609385
Actinotrichia robusta Itono	–	S- L. Liu and S. M. Lin/ 1 Apr. 2003	3rd Nuclear Power Outlet, Kenting National Park , Taiwan		AY688011
	CNU 32279	K. Lewmanomont / 6 Apr. 2010	Similan I., Phang Nga, Thailand	KC609386
Dichotomaria apiculata (Kjellman) Kurihara et Masuda	SAP 095732	16 Jun. 2002	Reihoku , Amakusa , Kumamoto Prefecture, Japan		AB117635
	TUNG 05369	S.- M. Lin and S.- L. Liu/21 Jul. 2002	Sail Rock, Kenting National Park, Taiwan		AY688020
	CNU 32163	3 Dec. 2002	Sungsan, Jeju, South Korea	KC768178
Dichotomaria australis (Sonder) Huisman, J. T. Harper et G. W.	SAP 101111	A. Kurihara and S. Shimada / 28 Nov. 2003	No. 16 Beach, Rye, Victoria, Australia		AB258443
Saunders	SAP 101108	A. Kurihara and S. Shimada / 4 Dec. 2003	Jervis Bay, New South Wales, Australia		AB258440
Dichotomaria diesingiana (Zanardini) Huisman, J. T. Harper et G. W. Saunders	–	M. Hommersand / 9 Jul. 1993	Sharks Bay, Port Alfred, Cape Province, South Africa		AY688026
Dichotomaria falcata (Kjellman)	–	24 Jul. 2001	Toji, Shimoda, Shizuoka Prefecture, Japan		AB117629
Kurihara et Masuda	CNU 032192	K. M. Kim/ 31 Jul. 2009	Oura Bay, Shimoda, Japan	KF752527
Dichotomaria hommersandii S.- L. Liu et S.- M. Lin	–	M. Hommersand / 20 Jul. 1993	Riet River, Port Alfred, Cape Province, South Africa	KC253901	JX072968
Dichotomaria huismanii C. W. Schneider, Popolizio et	CWS / CEL / TRP 10-5 - 13 [ BDA 0024 ]	C. W. Schneider , C. E. Lane, T. R. Popolizio / 19 Aug. 2010	Off Frick’s Beach , Tucker’s Town, Bermuda I., Bermuda (10–12 m)	KU321660
Spagnuolo	TRP 12-117- 5 [ BDA 1492 ] (holotype)	T. R. Popolizio / 20 Sep. 2012	Hog Breaker , north shore Bermuda I., Bermuda (12 m)	KU321661	KU321674
	TRP 12-151 - 11 [ BDA 1669 ]	T. R. Popolizio / 16 Nov. 2012	Southwest of North Rock , Bermuda I., Bermuda (12 m)	KU321659
Dichotomaria intermedia	WRT 1934 -164	W. R. Taylor / 17 Jan. 1934	Isabela Island , Galapagos I., Ecuador		KF752506
( R. C. Y. Chou) Wiriyadamrikul , M. J. Wynne et S. M. Boo	CNU 032199	K. M. Kim / 24 Oct. 2009	Gerupuk, Lombok, Indonesia	KF752532	KF752509
Dichotomaria latifolia ined. ( Galaxaura latifolia Tak. Tanaka)	–	S.- L. Liu and W. L. Wang / 25 Jan. 2003	Tahsianglan, Taipei County, Taiwan	KF752529	AY688021