Cucurbit Genetics Cooperative Report 3:55-59 (article 32) 1980

Problems with the Identification of Cucumis L. taxa

L. van Leeuwen and A.P.M. den Nijs

Institute for Horticultural Plant Breeding, Wageningen, The Netherlands

The Cucumis-working group at our Institute attempts to introduce resistances of several African species of Cucumis L. into the cultivated cucumber C. sativus L. We have, therefore, collected a large number of species from all over the world. The identification of Cucumis species, either collected directly in the wild or maintained under cultivation, often appears to be difficult and many received accessions need to be renamed by our taxonomists.

In 1976, 76 accessions were examined, 25 of which had to be reclassified. The high number of misclassifications is not surprising, since results of taxonomic studies of the genus are often incomplete or contradictory. Many authors made description based on single plants or small groups, or only on herbarium specimens. The latter is certainly not sufficient since the material, as we studied it in the herbaria of Kew (UK) and Leiden (Netherlands) is often incomplete. Roots or rootstocks are largely lacking although they are important for determining the life cycle, which can be an important character in some cases. Even fruits are often lacking although they are decisive in the identification. Spirit collections are very poor or nonexistent. Also, the leaves of especially the older specimens may be untidily mounted on the sheets s that one cannot even recognize their shapes. More than one taxonomist appears to have been frustrated by the lack of live material as is shown by frequent amendments of earlier descriptions, sometimes leading to embarrassing changes. One can find different descriptions of, for example, Bryonia callosa Rottl (1903) later placed in the genus Cucumis by cogniaux (1) as Cucumis callosus (Rottl) Cogn. (1916), which is considered synonymous with C. trigonus Roxb. by Clarke (1897). The description of C. myriocarpus Naud. by Meeuse (2) is completely different from the original one composed by Naudin (3).

The existing descriptions cover only a small part of the intraspecific variability. Therefore, many taxa were labeled species, which to us seem to be only subspecies, varieties, or just synonyms. Cucumis hardwickii Royle was named a variety by Alefeld [C. sativus var. hardwickii (Royle) Alef]. The original form has never been found after Royle described it, and plants resembling Royle's description are thought by Filov, amongst others, to be formae of C. sativus L. Naudin, after studying live plants in his garden besides herbarium material, has pooled many taxa, reducing many specific names to synonyms.

The identification of wild Cucumis species under conditions of cultivation poses its own problems. Plants grow in a glasshouse at Wageningen proved to be much larger and more luxuriant, which affects he sizes of all plant parts and possibly also leaf shapes. Ripening of fruits undoubtedly proceeds in a different way. We have, for example, never observed fruits of C. africanus L.f. and C. myriocarpus Naud. turn brown when maturing, although they are supposed to do so. We attempt to grow the plants under very poor conditions, but these will never be a replica of those prevailing in nature.

Thus the identification of Cucumis species is made difficult by inadequate descriptions and different growing conditions, with the result that the interpretation of names of Cucumis taxa varies from one worker to another. To solve this problem, we propose to adopt the following principles.

1. A consistent use of the available information from the literature can save much confusion. A Latin name without the name of the author is not sufficient. For example, one could mistake C. prophetarum Jacq., which is a synonym of C. myriocarpus Naud., for C. prophetarum L. When a description has been amended by a later author, this should be mentioned and pertinent literature should be cited.
2. Sometimes the variability of certain plant characters clearly trespasses the boundaries set by the available description of the taxon. In these cases we propose to make a description to which can be referred in future work, not with the intention to describe a new taxon, but to give a true image of the plants dealt with. If describing is not possible, one should add a question mark or an indication such as "received as. . .".
3. At least some plants to be classified should be grown under conditions resembling those in their habitat. Certainly a note about the growing conditions would be of value.

The collection of the North Central and Southern Regional Plant Introduction Stations at Ames (Iowa, USA) and Georgia (USA), respectively, is widely used. We think that several accessions of the PI collection studied at our institute needed reclassification. Because we feel it is worthwhile that all workers concerned have the, in our opinion, correct names at their disposal, a list of the PI numbers with their taxonomic classifications is given in Table 1. The pertinent literature for the identification is included.

PI classification*	Origin as given at PI lists	PI no.	IVT genebank no.	IVT remarks	Literature no.
Cucumis africanus	S. Africa	203974	1785	C. africanus L.f.	8
"	S. Africa	274036	1986	no flowers
"	S. Africa	299569	1787	C. africanus L.f.	8
"	S. Africa	299570	1457	C. africanus L.f. Seed sample received in 1974. See C. zeyheri Sond. 299570	8
"	S. Africa	299572	1053	C. zeyheri Sond.	5
"	U. S. A.	374151	1788	not C. africanus L.f.; seed like C. myriocarpus Naud.
C. anguria L.	Brazil	196477	0307	C. anguria L.	2
"	Ethiopia	233646	0310	C. anguria L.	2
"	S. Africa	282442	1790	not C. anguria L.; no flowers
"	Iran	386029	1791	C. melo L.	1
"	Iran	386031	1792	C. melo L.	1
"	Iran	386086	1793	C. melo L., much variation in fruits	1
C. dinteri	U. S. A.	374208	1794	no fruits
"	U. S. A.	374209	1795	no fruits
C. dipsaceus Ehrenb.	Ethiopia	193498	0255	C. dipsaceus Spach ex Ehrenb.	7
"	Ethiopia	236468	1170	C. dipsaceus Spach ex Ehrenb.	7
C. ficifolius A. Rich.	Ethiopia	196844	0870	C. ficifolius A. Rich	1
"	Ethiopia	203915	1984	C. ficifolius A. Rich; fruit like C. myriocarpus Naud.
"	Ethiopia	273648	1796	C. ficifolius A. Rich.	1
"	Ethiopia	280031	1797	not C. ficifolius A. Rich
C. heptadactylus Naud.	S. Africa	282446	1798	C. heptadactylus Naud.	1
C. leptodermis Scweik.	U. S. A.	374152	1799	no germination
C. meeusii	U. S. A.	376068	1800	C. meeusii C. Jeffrey	6
C. melo var. agrestis	Texas	140471	1746	C. melo var. agrestis Naud.	1
"	India	183311	0309	C. melo var. agrestis Naud.	1
C. membranifolius	Ethiopia	273650	1801	possibly C. ficifolius A. Rich.
C. metuliferus E. Meyer	S. Africa	202681	1730	C. metuliferus Naud	1, 7
"	Transvaal	292190	1802	C. metuliferus Naud.
C. myriocarpus Naud.	S. Africa	282447	1007	C. myriocarpus Naud., the same as C. zeyheri Sond. 299568
"	S. Africa	282449	1676	C. myriocarpus Naud.	8
"	S. Africa	299568	1051	not C. myriocarpus Naud., the same as C. zeyheri Sond. 299568
C. prophetarum L.	Ethiopia	193967	1729	C. ficifolius A. Rich.	1
C. pustulatus	Ethiopia	273649	1803	C. ficifolius A. Rich.	1
"	Nigeria	343699	1804	C. figarei Naud. es Del.	7
C. sativus L.	India	165506	0630	C. sativus L.	2
"	Turkey	167043	0632	C. sativus L.	2
"	Turkey	271337	1829/1830	C. sativus L.	2
C. hardwickii	India	215589	0777	segregating
C. sativus var. sikkimensis Hook.	India	165499	0629	C. sativus var. sikkimensis Hook.	3, 4
"	India	165509	0631	C. sativus L.	2
"	Turkey	169304	0642	C. sativus var. sikkimensis Hook.	3, 4
C. trigonis Benth.	India	271337	1805	C. sativus L. type
C. zeyheri Sond.	S. Africa	282450	1008	C. myriocarpus Naud.	8
"	S. Africa	299568	1806	not C. zeyheri Sond., the same as C. myriocarpus Naud. 299568
"	Natal	299570	1807	C. zeyheri Sond. Seed sample received 1978. See C. africanus L.f. 299570	5
"	S. Africa	299571	1052	segregating
C. species	India	183310	0308	no germination
"	Burma	200817	0460	C. melo L.	1
"	India	214050	1808	possibly C. melo L., no flowers
"	S. Africa	409732	1809	C. zeyheri Sond.	5
"	S. Africa	409733	1810	not Cucumis L. at all

* We have not always been able to obtain the author's abbreviation used by the PI Station.

Table Literature

1. Meeuse, A.D.J. In: Codd, L.E. 1965-1966. Bothalia 8:59-82.
2. Cogniaux, A. In: Engler, A. 1916. Das Pflanzenreich IV.275.I:143-146, 148-150.
3. Gabaev, S.G. 1929-1930. Ogurtsy Azii (Cucumbers from Asia). Trud. Priklad. Bot. Gen. Sel. 23(3):443-473.
4. Gabaew, S. 1933. Systematische Untersuchungen an Gurkenarten und Varietaten. Angewande Boanik 15:290-307.
5. Harvey, W.H. and O.W. Sonder. 1861-1862. Flora Capensis 2:496.
6. Jeffrey, C. 1965. Further notes on Cucurbitaceae. Kew Bull. 19(2):215-233.
7. Jeffrey, C. In: Milne Redhead, E. and R.M. Polhill. 1967. Flora of Tropical East Africa. (Cucurbitaceae):94-108.
8. Naudin, M. Ch. 1859. Ann. Sci. Nat. 4, Ser. XI:20-23.

Literature Cited

1. Clarke, C.B. In Hooker, Sir J.D. 1879. Flora of British India II:619.
2. Cogniaux, A. In Enger, A. 1916. Das Pflanzenreich IV.275.I:129-130.
3. Filov, A. 1964. Dikij rodich ogurtsa (The wild parent of the cucumber). In Bjull. Glav. Bo. Sad. 52:105-106.
4. Meeuse, A.D.J. In Codd, L.E. 1965-1966. Bothalia 8:74-76.
5. Naudin, M. Ch. 1859. Ann. Sci. Nat. 4, Ser. XI:1-86.
6. Rottler, J.P. 1803. Neue Schriften Gesellschaft Naturforschender Freunde zu Berlin 4:209-210.