The Journal of Indian Botany/Volume 1/March 1920/Variation in Bombay STRIGAS
VARIATION IN BOMBAY STRIGAS.
BY
W. Burns, D. Sc.,
Economic Botanist, Dept. of Agriculture, Bombay.
The present paper is a preliminary note embodying scattered observations on variation in species of Striga found in the Bombay Presidency.
In the course of the writer's investigation of the flora of Indian grasslands he frequently found Striga species. Many of these seemed to be imperfectly described in floras. A closer study of these species was therefore made. It will be convenient to take these one by one.
I. S. lutea : A species of wide geographical distribution, given in the floras of Hooker and Cook for India, Trimen for Ceylon, and Mueschler for Egypt. Pearson mentions its occurrence in South Africa where it is a serious pest on maize. In the Bombay Presidency it is a pest of jowar (Andropogon Sorghum) and bajri (Pennisetum typhoideum).
A. In these floras, in the species keys and descriptions the number of calyx ribs of the species is given as follows:
- Hooker: Key, 10-15; Description, 10-ribbed, rarely 15-ribbed,
- Cook: Key, 10-15 ribbed, ribs of the calyx most commonly 10; Description "Calyx . . . with one strong hirsute rib running from the base of the calyx to the apex of each tooth, and with 1 (less commonly 2) secondary ribs between them, which terminate at the sinus."
- Trimen: Key and description, 10.
- Mueschler: Key 10-17 ribbed; 10 ribbed; Description, generally 10 ribbed.
- Van Buuren, a graduate of the Poona College of Agriculture, and now in the Ceylon Department of Agriculture, in his paper[1] on Root Parasitism in Some Scrophulariaceae of Western India, states that S. lutea is usually 10 to 12 ribbed.
The above descriptions would seem to indicate a certain amount of variation in the number of calyx ribs, and the writer has found this to be the case in even the small number of specimens studied by him personally. 11 ribs are common. One plant gave flowers having respectively 11, 14, and 13 ribs. Another gave 11 and 13, and two others 14 and 13 on each plant. On one plant 15 ribs were found in one calyx. It is to be noted that additional ribs are never obtained by the increase of the number of main ribs but always by the intercalation of additional secondary ones. If there is only one additional secondary rib that has been always found in an anterior position (fig. 1).
The case of the 15-ribbed plant is shown in fig. 2. 10-ribbed cases were found in many plants collected from Karjat, a station on the line between Bombay and Poona, but few were found among those collected actually at Poona.
B. The colour of the corolla of S. lutea is given as follows :
- Hooker: "Scarlet, purple, yellow or white."
- Cook: "Usually bright yellow, occasionally red or white."
- Trimen: "Bright chrome yellow,"
- Mueschler : "Scarlet, red, yellow or white."
Van Buuren, in an MS. note dated Oct. 21, 1913 says "Corolla in early stages white, becomes a light chrome yellow when older or sometimes chrome yellow."
L. J. Sedgwick, writing to me on 3-9-19 states "The fact that S. lutea could be any other colour than yellow had escaped my notice. . . . It is always yellow in the Dharwar Malnad and the Nilgiris." Writing to me later on 15-11-19 the same botanist says ":As regards S. lutea, Bell swears to having seen the red-flowered form once at Ekambi in Kanara."
The corolla colours observed by the present writer are two (1) a sulphur yellow in plants found in grassland at various places, this colour of corolla has never, up to date, been observed by the writer in plants parasitic on crops; (2) a faintly creamy white, slightly deeper in colour at the throat, in plants parasitic on jowar, bajri, and grasses.
The writer has never seen a red or a purple. There is some probability that Hooker's purple is a description of the bluish tinge which the corolla, and in fact, the whole plant, take on very soon after being plucked.
C. The anthers are not described by any of the botanists whose floras have been mentioned. The anthers in S. lutea are brownish-yellow in both white and yellow varieties. The colour of the anthers is an aid to distinguishing the white variety from S. densiflora. In S. densiflora the anthers are bluish-black.
With reference to the yellow variety the writer would quote the following footnote from Van Buuren :
"Since the publication of this, a specimen which is very similar to Striga sulphured according to the description given by Cooke was found in the grass lands at Alibag on
the banks of a tank. It can hardly deserve rank as a new
species, being apparently a small form of S. lutea. The
corolla is of a deep yellow colour."
The present writer has never seen $. sulphurm. h. J. Sedgwick
in a letter mentions it as a rare plant found during the monsoon in
the Malnad, and says he has specimens.
II. S. densiflora : This is described in all floras as having a 5-ribbed calyx and the writer has found no exceptions to this rule. The 5 primary ribs exist and there are no secondaries.
The corolla is variable in size and shape (fig, 3). The following table gives a comparison of the tube length, anteroposterior and lateral diameters of the flowers of S. lutea and <S. densiflora.
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a b, These two plants were growing within a foot of each other. All flowers on one plant of uniform type.
The curve in the tube of S. densiflora is much more marked than in that of S. lutea (fig. 4.) Hence the 10 + 3, &c. in the tub- length measurements of the former 10 being the measurement below and 3 above the bend Van Buuren in his MS. note states that the S. densiflora tube is " strongly bent above the middle ".
As above mentioned, the anthers of S. densiflora are bluish black. The writer was at first suspicious that this colour was merely an early appearance of that blueing to which all Strigas are subject after plucking. Dissection of young flowers on the living plant however, dispelled this suspicion and showed that bluish-black is the natural colour of the anther.
Specimens from different areas sometimes differ. Thus a plant of S. densiflora from Chharodi in Gujarat showed close packing of the flowers due to a [shortening of the internodes, and increased scabridness with more serration of the leaves when compared with S. densiflora collected in Poona.
The writer has found S. lutea and S. densiflora growing together both in grass and on crops. This is also recorded by Barber and bv Van Buuren. III S. euphrasiodes:—The writer was for a long time unable to find this species in any grassland round Poona, although one specimen in the Poona herbarium had been collected at Pashan, a near-by village. At length a very few specimens were found in the area of waste land near the College of Agriculture in a piece of that land adjoining an irrigation distributory. At Chharodi in Gujarat this species was the common one, with occasional S. densiflora and no S. lutea, while at Tegur in the Dharwar District S. euphrasiodes was the only species found.
Van Buuren reported it on roots of grasses of the irrigation channel of the College Farm at Poona, and considered it more hygrophilous than the other species mentioned.
The diagnostic character of this species is the possession of 15 ribs, each main rib having on each side of it a secondary rib which runs right up to the tip of the calyx tooth.
Here again there is some variation in number, all the Chharodi specimens having 16 ribs, the additional rib being, as usual, anterior.
The writer came across one plant pink in the bud and also in the fully expanded corola. Van Buuren states: "At the approach of the dry season some plants which I had under observation showed a sensitiveness to drought. The leaves took on a purplish-red tinge while even the corolla had many fine streaks of the same colour, doubtless due to anthocyanin pigments."
The corolla length was found to be very variable with reference to the calyx length. No measurements were made.
IV. S. orobanchoides:— This is a well marked holoparasitic species in which the writer has noted no striking variations. It is net common in ordinary grasslands, the few specimens that the writer has seen being from a forest reserve en a hillside near Poona.
Conclusion
The Scrophulariacece is an order with apparently a history of variation, if one may judge :by the sub-orders, classes and genera into which it is divided. Striga itself provides what is apparently a recent mutant. Strigina, described by Engler[2] differing from Striga in having the two anterior stamens reduced to staminodes. The question arises : Are the two colour forms of S. lutea and the plants with different sizes and shapes of corolla in S. densiflora to be put in different species? The only answer to this question can be got by growing the plants in pure culture, and up to date the writer has not succeeded in germinating Striga seed either by itself or in contact with host roots.