DOCKS AND SORRELS OF ESSEX
267
2. Stems procumbent with erect flowering branches. Leaves all
narrow linear up to ten times as long as broad, their edges often
revolute. Mature nut 0.9-1.3 mm. long by 0.6-0.8 mm.
broad .................. R. tenuifolius
2. Stems erect. Leaves lanceolate or linear-lanceolate, broader
than in the previous species, plane. Mature nut 1.3-1.5 mm.
long .................. R. Acetosella
SUBGENUS II. ACETOSA.
2. R. Acetosa L. Native. Common Sorrel. Common in meadows
and on roadsides throughout Essex (v.-cc. 18 and 19). The male
flowers are often overlooked as the plants on which they are borne
are less numerous than the female. Moreover, the stems of the
female plants continue to lengthen after fertilisation so that the
fruits are carried up to a higher level and are therefore more
prominent amongst the surrounding grasses. Although not yet
detected in Britain it is quite possible that R. thyrsiflorus Fingerh.
may yet be found as it occurs in Holland and Scandinavia. In this
species the branches of the inflorescence are repeatedly divided as
compared with the almost simple panicle branches of R. Acetosa.
Essex botanists should look out for this allied species.
SUBGENUS III. LAPATHUM.
3. R. triangulivalvis (Danser) Rech.f. Alien. Willowleaved Dock.
A native of Canada and the United States which occurs rather
frequently as an alien in northern Europe (including the British
Isles) and has often passed as R. salicifolius. It is recorded from
Dagenham and Grays (Melville and Smith, B.E.C. 1927 Rep., 453,
1928) and I have seen material from Dagenham (Brenan (4078),
Hubbard, Summerhayes, and Turrill, 1929, and 1937, Hb. Kew)
and Tilbury (Melville, 1926, Hb. Nat. Mus. Wales). These locali-
ties are all in v.-c. 18. The records for North Essex require
revision—see next species.
4. R. altissimus Wood. Alien. Rather closely allied to R.
triangulivalvis and most easily distinguished by the broader leaves
(ovate-lanceolate as compared with linear-lanceolate), which are
broadest below the middle, and the larger valves which exceed
4.5 mm. in length. In 1944 I suggested (B.E.C. 1941-2 Rep., 576
and 582) that some at least of the specimens from Hythe Quay,
Colchester, v.-c. 19, were likely to belong to this species, and Dr.
K. H. Rechinger has now confirmed the identification (Candollea,
11, 240, 1948).
R. longifolius DC. This species occurs in northern England and
Scotland and is unlikely to be found in Essex. It is mentioned here
because the name has been applied erroneously to R. Patientia
in the county. See below.
5. R. Patientia L. Alien. Patience Dock. A native of south-east