Spirodela

ESSEX BOTANY AND MYCOLOGY GROUPS

Spirodela

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Spirodela polyrhiza (L.) Schleid. Greater Duckweed ___________________________________________________________________________________

Plant body flattened, orbicular, up to 10mm long, with (5)7-15 roots and 7-12(15) veins. Bright green early in the season, usually purple below, and acquiring a purple rim above in the summer. Often completely reddish-purple in late autumn after a high U.V. flux summer. Has a circular membranous scale folded around its basal end that may be penetrated by a few of its roots. A sporadic plant, only known to flower or set seed once in the U.K. and therefore reliant on sticking to bird’s feet, amphibian’s skin and aquatic mammal’s fur for dispersal. Perennates by budding off rootless, brownish, bean-shaped turions, 1-2mm long that sink in autumn and rise again in the spring. Nationally, occurs north to Lancashire in the west and to Northumberland in the east, with a thin scattering of records further north in the Scottish lowlands. Said to have been more widely distributed in the past. Seems to have critical requirements however, as it seldom persists at a site for more than a few years. Abundant in some years, and widespread, at other times almost apparently extinct. Several ponds with just a few fronds in 2009 suddenly experienced population explosions, culminating in 2011 when several of them were completely covered. Possibly doesn’t like ponds which are drying up and getting too eutrophic, and seems to do best in wet springs and summers. Occurs in ponds, lakes, canals and slow flowing rivers and streams in well lit, fertile, weakly acid to weakly basic waters, and in weakly brackish coastal dykes. Doesn’t seem to persist at one site for long, so the dot map and records list will give a false impression of its distribution at any one time. Said to be hardy down to -37^oC. U.K. distribution possibly limited by combination of the need for near neutral to weakly basic waters and a minimum summer temperature of around 16^oC. Widespread in N. & C. America, Europe, Asia and N. Australia. Scroll down for records.

POST 1930 RECORDS:

TQ(51)38	350,877 ?	18	Walthamstow Marshes, 1979. Brian Wurzell.
	394,886	18	Epping Forest, Hollow Pond. Leyton Flats. 1981. Paul Ferris.
	389,889	18	Cow Pond, by Whipps Cross roundabout. 12 June 1987. K.J.Adams.
	394,888	18	Epping Forest, Leyton Flats, the Model Boat Pond. June 2015. K.J Adams.
	3931,8911	18	Snaresbrook, The Round Pond. May 1970. K.J.Adams.
TQ(51)39	39,94	18	Chingford, nr. Queen Elizabeths Hunting Lodge. Pre 1974. Flora of Essex. Jermyn.
	3956,9110	18	Oak Hill, Napier Arms in second pond from road. 24 Sept 1980. K.J.Adams.
	3951,9105 & 3956,9110	18	Oak Hill, Napier Arms in first two ponds from road. Sept 1984. K.J.Adams.
	39,92	18	Hyams Park Lake. Sept 1985. K.J.Adams.
TL(52)30	380,016	19	Waltham Abbey, Cornmill Stream SSSI. 10 August 1983. Brian Evesham.
TQ(51)48	408,872	18	Shoulder of Mutton Pond, Wanstead Park. 30 June 1987.K.J.Adams.
	415,861		Wanstead Park, Heronry Pond, just two fronds. 31 May 2005. K.J.Adams.
TQ(51)49	424,974	18	Epping Forest, Baldwins Hill Pond.
	429,981 & 428,979	18	Epping Forest, Goldings Hill north and south ponds. July 1969; in both ponds, 3 September 1978. Kenneth J Adams.
	429,981	18	Epping Forest, Goldings Hill north, abundant, 8 August 1981. K.J.Adams.
	4091,9659	18	Epping Forest, Fairmead Plain Pond. 1972. K.J.Adams.
	418,985	18	Epping Forest, Wake Valley Bomb Crater Pond. Pre 1974. Flora of Essex. Jermyn.
	418,985	18	Epping Forest, Wake Valley Bomb Crater Pond. 8 August 1981. K.J.Adams.
	420,987	18	Epping Forest, Wake Valley Pond. Pre 1974. Flora of Essex. Jermyn.
			Epping Forest, Little Wake Valley West pond, and the V2 Crater pond, June 1968. KJA.
		18	Epping Forest, Little Wake Valley West pond, and Little Wake Valley East ponds. 8 August 1981. K.J.Adams.
	404,953	18	Connaught Waters, northern end. 22 June 1986. K.J.Adams.
	4127,9829	18	Epping Forest, Oak Pond north, July 2009 a few odd thalli; July 2010 increasing; July 2011 abundant; completely blanketing pond surface July 2015. K.J.Adams.
		18	Epping Forest, Earl's Path Pond, scarce. 29 July 1981. K.J.Adams.
	47,92	18	Hainault Forest, lake. Pre 1974. Flora of Essex. Jermyn.
TL(52)40	478,086	19	Harlow Common new pond. 18 July 1991. K.J.Adams.
	4736,0918	19	Potter Street, Kingston Lane Pond South. 16 July 2011. Colin Austin & K.J.Adams
TL(52)41	4783,1122	19	Old Harlow, Tumulus Pond. 16 July 2011. Colin Austin & K.J.Adams
	420,113	19	Hunsden Mill. Pre 1974. Flora of Essex. Jermyn.
	40,10	19	R. Stort at Roydon. Pre 1974. Flora of Essex. Jermyn.
	483,137	19	Sheering, R. Stort backwater, sparingly with Lemna minor. August 1980. K.J.Adams.
TL(52)43	47,31	19	Clavering, village ponds. Pre 1974. Flora of Essex. Jermyn.
TQ(51)59	523,908?	18	Romford Golf Course. Pre 1974. Flora of Essex. Jermyn.
	547,931	18	Dagnam Park, Hatter’s Wood SE large pond. 24 June 1979.K.J.Adams et al.
	548,927	18	Dagnam Park, Oval Pond West. 24 June 1979. K.J.Adams et al.
	57,94	18	South Weald Park. Pre 1974. Flora of Essex. Jermyn.
	57306,94150	18	South Weald Park. In small pond. 4 September 1981. K.J.Adams.
TL(52)50	511,082	19	Magdelan Laver, pond nr church. Pre 1974. Flora of Essex. Jermyn.
TQ(51)68	626,898	18	Thorndon Park South, Mill Wood Lake, August 1980. K.J.Adams.
TQ(51)69	63,96	18	Hutton Wash. Pre 1974. Flora of Essex. Jermyn.
TL(52)63	610,317	19	Thaxted, pond nr Fox & Hounds.Now infilled. Pre 1974. Flora of Essex. Jermyn.
TQ(51)78	7380,8634	18	Wat Tyler C.P. teaching pond. 14 July 2011. KJA.
TL(52)70	77,08	18	Little Baddow, marsh by R. Chelmer. Pre 1974. Flora of Essex. Jermyn.
	7891,0638	18	Little Baddow Heath, abundant with L. minuta. 21 June 2011. K.J.Adams.
TL(52)71	703,100	19	Broomfield, pond. Pre 1974. Flora of Essex. Jermyn.
	71,11	19	Little Waltham. Pre 1974. Flora of Essex. Jermyn.
TL(52)74	72,42	19	R. Stour nr Baythorne End. Pre 1974. Flora of Essex. Jermyn.
TQ(51)88	81-2,85	18	Hadleigh Marshes, pond. Pre 1974. Flora of Essex. Jermyn.
TL(52)81	82,18	19	Rivenhall Place lake.
TL(52)82	81,23+	19	Bradwell, mill stream Pre 1974. Flora of Essex. Jermyn.
	821,315-17	19	Halstead, pond on edge of sports field at Star Style. 9 July 1993. Matthew Shepherd.
TL(52)84	81,46	19	Pentlow, ditch by R. Stour. Pre 1974. Flora of Essex. Jermyn.
TQ(51)98	95,87	18	Wakering Common. Pre 1974. Flora of Essex. Jermyn.
TQ(51)99	93,96	18	Creeksea, pond and stream. Pre 1974. Flora of Essex. Jermyn.
TL(51)92	99,20	19	Roman River Valley survey. 1983. C.N.HS.
TL(51)93	90,33	19	Bures, ditch by R. Stour. Pre 1974. Flora of Essex. Jermyn.
TM(62)00	00,06	18	Bradwell, pond at Bacons. Pre 1974. Flora of Essex. Jermyn.
TM(62)02	00,02	19	Roman River Valley survey. 1983. C.N.HS.
TM(62)03	04,33	19	Dedham Vale, Bridge Farm. 4 August 2015. Terri Tarpey.
	05,33	19	Dedham Vale, Bridge Farm. 4 August 2015. Terri Tarpey.
TM(62)12	18,21	19	Thorpe le Soken, 2 August 1984. Jerry Heath & Terri Tarpey.
TM(62)21	20,18+	19	Holland Brook. Pre 1974. Flora of Essex. Jermyn.
	20-1,17	19	Great Clacton, Pickers Ditch. Pre 1974. Flora of Essex. Jermyn.
	219,173	19	Holland Haven, a few plants in brook by sewage works. 20 August 1997. Anne Guiver & Terri Tarpey.
	22,17	19	Holland Haven. 1989. CNHS.

Pre 1930

TQ48

18

Snaresbrook. G.S.Gibson.

TQ49

18

Woodford, common. Richard Warner.

TQ58or68

18

Warley Common. Daniel Cooper.

TL50

18

High Ongar. William Hind.

TL53

545,368

19

Herbert’s Farm. G S Gibson.

TL53or54

19

Walden, rare. G S Gibson.

TQ89or99

18

Ponds nr. Canewdon. Henry Ibbotson.

TL80-81,08

18/19

Chelmsford, nr, Barnes Mill. Alfred Greenwood.

TL81or82

19

Coggeshall. Dr E Varenne.

TL81or82

19

Kelvedon. William Hind. & Dr E.Varenne.

TL82

19

Halstead, rare. Thomas Benthall.

???

19

Ditches by the Stour. W.H.Coleman.

TM03

19

Dedham, frequent. W.H.Coleman.

TM23

19

Harwich. W.W.Newbold.