Parthenium hysterophorus. L : Morphological studies.
Endale Berhe
Kombolcha Plant Health Clinic, South wollo, Amhara region, Ethiopia.
e-mail k-phc@telecom.net.et
Introduction
Parthenium is a herbaceous annual plant belonging to the Asteraceae (Compositae) family, sub family
Tubuliflorae (1,6), and tribe Heliantheae (5).
Parthenium is known for its allergic effect on humans and alleged to have allelopathy on plants.
The major chemical composition implicated in allergy and allelopathy is the sesqiuterpine lactone group
(7,8). Sesquiterpine lactones are also anti- feedant, deterrants of oviposition and growth inhibitors (9).
Among the various members of sesquiterpine lactone parthenin is the most important.
However it is quite interesting to note that only five seeds are borne per head in spite of the large number
of disk florets per single flower head. On the other hand during a single observation as many as 11300
flower heads per plant have been counted (personal observation). This is tantamount to at least 56500
seeds per single parthenium plant. However considering the indeterminate flowering habit, and extended
period of flowering a single parthenium plant during its entire life time can bear a minimum of 75000 seeds.
On the other hand losing so many potential seeds per flower head seems a little irrational for natural
phenomenon. Definitely there has to be some major strategic importance to justify the trade off.
As it is the rate of spread is so high and inconvenient for chemical control and hand pulling campaigns
to be successful in containing parthenium.
Among others the striking plasticity as expressed in leaf dimorphism and orientation at different growth
stages; its capability to bear seeds as early as within a month time after germination; and extended period
of flowering beyond 14 months since the first flowering (personal observation) require further study before
to come up with an effective control strategy.
To date the literature on parthenium distribution, harmful effects, and biocontrol is vast. Nevertheless
details on the botany especially flower morphology and their role in reproduction is scanty.
Therefore the main aim of this study was to fill the information gap felt necessary to devise an effective
control strategy.
Material and Methods
Germination was observed in four petridishes by placing seeds between layers of filter paper.
Four seedling trays filled with soil were also used to grow parthenium seeds for observation of vegetative
characteristics. Fresh parthenium seeds collected from the road sides of Kombolcha town were used for
all examinations.
Most of the examination of floral parts and others was made using a binocular and stereo microscope.
As the floral parts, particularly the disk florets were tightly packed and with high fluid content the flower
heads were soaked in 95% ethyl alcohol for about an hour and stained with Aniline blue , before
examined under binocular microscope.
1
Result and Discussion
I.
Seeds and germination
Parthenium seeds have inverted cone shape & rough black surface measuring 2-3 mm in
length and 1.25 mm in diameter at the widest end. Upon imbibitions the seed opens round
the edges. The seeds have a parchment like pappus at the wider (top) end.
Parthenium seeds were germinated within 15-20 days after planting (Annex-1).
II. Vegetative growth
a. shoot
When grown alone it shows a prostrated growth and relatively larger leaf blades at early seedling stage.
However, it turns up later to be erect.
b. Leaf
Parthenium leaf is simple with highly parted leaflets. The leaves grow alternately on the stem
and branches profusely. The midrib can measure 10-12cm long. It is light colored & concave up-ward with
a leafy outgrowth along its length between and before the leaflets ( Annex. 2).
The leaflets themselves are parted. The leaf petiole is clasping. In addition to its successive branching
from the main stem to form a broad canopy.
Another striking feature of parthenium is the leaf dimorphism. In contrast to the leaves with wider leaflets at
early seedling stage, parthenium plants at maturity will have their uppermost leaves almost skeleton zed.
It is conceivable that this leaf dimorphism could be an evolutionary development with a crucial role for
survival and success as a weed. Among the advantages is the high photosynthetic capacity at early
seedling stage which is vital for the establishment of a deep root system to insure survival of the
competition and moisture stress. On the other hand after maturity when there are enough number of
photosynthesizing leaves and further root growth is no more needed adjustment to facilitate the filtration of
light to the lower canopy would be more important as parthenium is a light loving plant (7).
c. Root
The other characteristic feature, which seem to contribute much to the survival and success of Parthenium
in the drought prone areas is its tap root system and extensive root development. Without which
Parthenium wouldn't have a chance to grow and bear seeds in the dry off season where most other
vegetations are not available in the field.
Almost the same root to shoot ratios, 9.42:1 and 9.52:1 were computed from parthenium plants grown in
pots with clay and sandy soils respectively (table-1) (Annex. 3).
Such a high root to shoot ratio and slow shoot growth at early seedling stage were typical features of
drought tolerant plant (10).
III. Flower
The flower is a white head with 5 ray florets, and about 40 disk florets. Commonly a
cluster of separate flower heads occur on a corymb which grow axially & terminally. The flower head
measures 3-4 mm in diameter. Flower heads are borne on a slender pedicel.
2
a. Disk florets
Several small, cylindrical, dull colored corolla tubes are packed tightly to form the creamy White Center of
the flower head. All the stamens seem to originate from the top of the ovary as the latter is epigynous. The
anther and stigma are brush like in appearance. There are four stamens per disk floret, which however
were found to shed their pollen before the stigma of the pistil opens The style is uniformly cylindrical
( Fig. 4). The pistil was also observed within the corolla tube below the anthers until it is ready for
fertilization. When ready the pistil grows above the tip of the corolla tube and anthers.
Later on from a study on pot grown parthenium plants where all but only a single flower head was allowed,
it was learned that that the pollen from the anther in the disk florets was capable of fertilization and seed
production with the ovule from the ray floret. The failure in the disk floret to bear seed is thus more likely
from the morphological incompatibility in the disk florets or factors related to the pistil.
b. ray flower
Only 5 ray florets were present per flower head. Unlike the disk florets, the ray floret had a white corolla
tube with pronounced lips. The ray floret is also a pistilate; There are no stamens. However they are
observed wide open most of the time. The stigma is brown, thick and two parted. The style is also relatively
shorter and thicker than is its counter part in the disk floret. The ovary was more or less oval and found
enclosed in a black fibrous material which could be mistaken for the seed owing to its shape color and
position at the base of the flower. (see Annex. 5)
It seems that the seeds are produced from the pollen grain of the disk floret and ovules of the ray floret.
IV. Other observations
Based on a survey data from around Kombolcha town parthenium plants with only a single shoot the
number of flower heads per shoot was found to be positively correlated to the shoot length (r = 0.76)
(p0.01). The shoot length also was positively correlated to the root depth (p0.01) (table 2) (fig-6). Owing
to the negative intercept and positive slope a threshold shoot height for initiation of flowering was
computed to be 3.01 cm. Based on this regression equation the change in number of flower heads (log) for
a unit change in shoot length (log) was 1.81 after the threshold shoot length. This figure was not far from
the pot study observation, 5 cm, the maximum shoot height attained by parthenium before the first
flowering.
The correlation between the number of flower heads and shoot length unlike the with a single shoot
parthenium plants was not significant. However the number of flower heads (log) was significantly
increased with an increase in shoot volume (log) (r2 =0.7) (p 0.05) (table-3) (fig-7).
Table 1 Mean shoot and root length (cm) of parthenium plants.
Details
shoot
root
clay soil
0.825
(0.185)
7.77
(1.68)
sandy soil
0.777
(o.171)
7.4
(2.2)
3
Table 2 Flower heads and shoot length from single shoot parthenium plants.
sample shoot length number of
sample shoot length number of
(cm)
flower heads
(cm)
flower heads
1
6.1
11
40
77
942
2
26
19
41
78.5
388
3
27
7
42
80
133
4
29.5
86
43
80
620
5
30
34
44
80.4
1635
6
34
120
45
81
947
7
34
46
46
81
256
8
35.6
77
47
81
674
9
42
301
48
82
785
10
44
86
49
84
804
11
49
186
50
85
1284
12
49.5
62
51
85
490
13
49.6
312
52
85
284
14
50
217
53
85.8
224
15
50.5
233
54
86
300
16
51
36
55
94
715
17
51.6
228
56
98
612
18
52
43
57
101
792
19
52
201
58
103.4
331
20
54
110
59
104
1408
21
56
122
60
106
554
22
56
312
61
108
1907
23
56
182
62
108
219
24
57
282
63
110
2633
25
58
120
64
112
2853
26
60
243
65
113
237
2
60
199
66
134
1121
28
60
518
67
137
618
29
63
194
68
138
477
30
65.2
354
69
138
278
31
65.5
185
70
146
262
32
67
351
33
69
272
34
69
295
35
70
327
36
71
909
4
37
75
415
38
39
76
76.2
318
608
Table-3 Parthenium flower heads and shoot volume
Plants shoot
shoot
flower height (cm) circumference (cm)
heads
volume
(cc)
1 185.11
308
2 397.39
1012
3 850.96
3785
4 447.13
2045
5 197.05
641
6 216.46
406
7 507.32
569
93
165
167
156
99
118
177
5
5.5
8
6
5
4.8
6
5
Reference
1. Robbins, W.W., T.B.Weier and C.R. Stocking 1961. Botany. Introduction to
plant sciences (2nd ed.). John Wiley & Sons Inc., New York.
2. Fenner, M.1985. Seed ecology. Chapman and Hall. London.
3. Holman, D.H and I. J. Dale. Parthenium weed threatens Bowen Shire.
Queens land Agricultural Journal. January - February,1981.
4. Parthenium hysterophorus. Department of Natural resource's Pest fact. Australia.
5. Navies, S.C., R. E. McFadyen, F. D. Panetta, S. W. Adkins, 1996. A comparison of the growth
and phenology of two introduced biotypes of Parthenium hysterophorus PP 313-316.
In: 11th Australian weeds conference. R.C.H Shepard (ed.). Weed science society.
Victoria. Frankston.
6. Peace Corps. Information collection & exchange. New crop production handbook.
Section I. Classification of Plants.
7. Fasil Reda. The biology and control of Parthenium. In: Rezene Fessehaie (ed.) 1991.
EWSC proceed of the 9th Annual conference. Addis Abeba.
8. An obnoxious weed-Parthenium hysterophorus. International Parthenium Research Group.
9. Philogene, B. J. R. and J.D.H. Lambert. Botanical pesticides: Optimizing pest control & minimizing
environmental impact.
10. Ashley, J. (1999). Food crops & drought. In: Coste, R.(ed.) The tropical Agriculturist.
Macmillan Education Ltd. London.
6
flower heads (log)
Fig-6 Parthenium flower heads (log) Vs shoot
length (log)
4.00
R2 = 0.58
3.00
2.00
1.00
0.00
0.00
0.50
1.00
1.50
2.00
2.50
shoot length(log)
flower heds (log)
Fig-7 Parthenium flower heads (log) Vs shoot
volume (log)
4.000
3.000
R2 = 0.71
2.000
1.000
0.000
0
200
400
600
800
1000
shoot volume (log)
7
Annex.1 Seed
Annex. 2 Leaves
Annex.3 Root
Annex. 4
Disk floret
Annex.5 Ray floret
8