Mystery Plant Project (Tagetes erecta)

Part A

Kelsey Kruse

Loras College

1450 Alta Vista

Dubuque, IA 52001

Around the summer months, one can take a walk around a garden in the Midwest and can

often smell a strong, familiar scent. This scent belongs to the common marigold (Tagetes erecta,

L.). Marigolds are old-fashioned, charming, and an enduring garden favorite, adding many

shades of bright yellows, oranges, and reds to brighten a garden.

Growth Form:

Figure 1. A fully bloomed

T. erecta L. plant.

The Tagetes erecta L. (the common marigold or the African marigold), is an annual,

herbaceous flowering plant (Figure 1). Annual meaning that it completes its life cycle in one

growing season, and is categorized as herbaceous because the plant does not possess a permanent

woody stem and the part of the plant that is above ground dies at the end of the growing season,

which is typically summer and autumn.(URL 2, 5)

Morphology:

The seeds of the T. erecta L. plant were long and skinny. They were dark brown/black in

color and possessed a white, fluffy tip (the pappus). T. erecta plants displayed epigeous

germination with the hypocotyls being bent and then straightening to raise two cotyledons above

the ground, approximately 5 days after planting. (Figure 2)

Figure 2. Emerged cotyledons.

Stem and Leaves

Our plants grew to an average height of 10 cm. However, marigolds will often grown to

heights nearing about 2 feet or more. (URL 2) This vertical growth was made possible by the

strong stem of the plant. The stem of the T. erecta plants was thin (.25 cm diameter) around the

bottom, smooth to the touch, hairless, dark purple at the base, and fades into a thicker (.35 cm

diameter), striated green as you go closer to the top. The stem branched off into multiple

different sections near the plant’s apex. As the leaves developed, they were also hairless, of

compound form with serrated margins. The leaves were oppositely arranged around the branched

stem (Figure 4). An individual leaf possessed up to 9 leaflets, arranged in an oddly pinnate

manner. Conspicuous glands were scattered on the underside of the leaflets (Figure 3) and,

especially when crushed, the leaves emit a highly fragrant smell. Leaflets are obuate (widest near

the apex), the tip is mucronate (small, abrupt points), and they possess netted, pinnatified

venation, with one main vein and many veins branching off of it (Figure 3). The leaf base can be

described as acuminate (or slightly tapering off into a point). Sizes of leaves varied from 5 cm in

length and 4 cm in width (from the widest leaf span) to 1 cm or less. The largest leaf was located

at the apex of the petiole and leaf size decreased as you neared the stem. The leaves had a

petiole, however, the individual leaflets lacked a pedicel and can therefore be classified as

sessile. The bases of the leaves also appeared to expand and connect along the main axis. The

leaves were green in color.

Figure 3. Underside of a leaf.

Figure 4. Aerial view of leaf

arrangement before flowering.

Root

Our plant, T. erecta, showed a tap root system of growth, having one primary root which

comes down and penetrates the soil with many lateral roots sprouting from the main one (Figure

5). The root functions in obtaining nutrients for the plant and bringing water and nutrients up to

the shoot of the plant as well as anchoring the plant in the soil. It also provides support for the

plant so it is able to grow vertically.

Figure 5. Tap root of T. erecta.

Based on the netted, pinnately-arranged leaves of the leaves, the tap root system, the

epigeous germination, and the flower petals being in multiples of 5, we can infer that our plant,

T. erecta, is a dicot.

Anatomy:

Stem

The stem of our plant was typical of many dicot plants. When the round stem was

dissected, the cross section showed an interior as displayed in the microscope picture below

(Figure 6). From the outermost part of the stem to the innermost part of the stem, the stem

possessed a single-layered epidermis, a cortex consisting of parenchyma tissue, a small section

of what could possibly be sclerenchyma (functioning in support of the stem), a ring of vascular

tissue (xylem) with secondary cell walls of the xylem cells, and a pith layer consisting of the

innermost parenchyma. (Figure 6) In the stem, there are multiple distinguishable vascular

bundles arranged in a ring between a thin pith layer and the cortex. This ringed xylem layer with

multiple vascular bundles is also an indicator that the plant is a dicot, for in monocot plants, the

vascular bundles are not arranged in a neat ring along the outer edge of the stem, but rather

scattered throughout the stem. Having the vascular bundles in the ring provides the function of

being able to distribute water and nutrients out to all of the branches and leaves. The ground

tissue in the stem is scattered and surrounds all of the separate vascular bundles, functioning in

being able to transport water and nutrients to the xylem and phloem.

Figure 6. Cross-section of T. erecta

stem, 100x magnification.

Root

The roots of the T. erecta were white and tough. Each plant had a tap root that produced

multiple lateral roots. When the root was cut for a cross section, the outermost purple layer

peeled off of the green inner layer. Figure 7 shows a cross section of the root of the T. erecta.

The root possessed a single layer of epidermis, a cortex consisting of parenchyma cells, and a

single, thick ring of vascular tissue (which made up the majority of the interior) with a small

circle of parenchyma cells in the center of it (pith). Because the vascular bundle is located in the

center of the root and the ground tissue is exterior to the vascular bundle but interior to the

epidermis, all of the ground tissue transports only to the one vascular bundle, which aids in

efficiency because the root’s function is to bring water and nutrients to the stem.

Figure 7. Cross section of T. erecta

root. 100x magnification.

Reproduction

Flower Structure

Figure 8. T. erecta

inflorescence.

T. erecta possesses a very complex flower structure. The flowers on this plant occur on

terminal buds. As it is of the family Asteraceae, the common marigold possesses an

inflorescence, or a flower head, for their corolla instead of a single flower (an inflorescence

refers to a conglomeration of numerous smaller flowers to give the appearance of one big

flower).The head of the common marigold is radiate, meaning that it contains both ray and disc

florets. (Figure 8) The receptacle is naked. There are six bracts arranged in one circle, united to

the apex. (Figure 8)

The ray florets are the outermost florets and have 2 awns, 1 petal, are pistillate

(possessing only the female reproductive structures), incomplete (not possessing all four whorls),

and imperfect (not possessing both male and female reproductive flowers). (Figure 9) They

possess two ovaries, as noted by the carpel with a tip separated into two sections. There are much

fewer ray florets than disc florets. The disc florets of T. erecta are staminate (containing only the

male reproductive parts), incomplete, and imperfect. (Figure 10)

Figure 9. Pistillate ray floret. Figure 10. Disc floret with

petals removed.

Although out plants possessed very vibrant yellow petals, the color of the common

marigold can range from yellow to a red-orange. (URL 2, 3, 5) One of our plants also possessed

faint purple nectar guides on the petals. (Figure 11)

Figure 11. Flower head

with nectar guides.

All four whorls are present, therefore making T. erecta a complete flower. It is also

bisexual and monoecious, seeing as it possesses both male and female reproductive structures. It

also displays radial symmetry.

Pollination

Having a flower head containing multiple flowerets helps to prevent self-fertilization and

promote cross-fertilization. The plant does this by ripening the reproductive structures at

different times. The ray florets will open up first, and then the disc florets will open. That means

that by the time the staminate disc florets of one plant open, the pistillate ray florets will most

likely have already been pollinated with pollen from a different plant. Because of the yellow

color, strong odor, and nectar guides, the marigold is most likely pollinated by bees. Bees are

attracted to colors, eat nectar, and have a strong sense of odor, which means the marigold would

be a perfect plant for them to pollinate.

Fruit

T. erecta L. produces achenes—or a simple dry indehiscent fruit containing a single seed

that nearly fills the pericarp but does not adhere to it. Our own plants did not produce these, as

they were not pollinated, but this could be seen in our seed.

Germination time/rate

Our T. erecta L. plants germinated in about 5 days. 18 of our 23 seeds germinated. The

plants flowered in an average of 2 months.

Taxonomy

Kingdom: Plantae (Plants)

Division: Magnoliophyta (Flowering Plants)

Class: Magnoliopside (Dicotyledons)

Order: Asterales

Family: Asteraceae (Aster family)

Genus: Tagetes L. (Marigold)

Species: Tagetes erecta L. (Common marigold) (URL 1)

Ethnobotany/ Economic Botany

T. erecta L. is often used in gardens to protect the rest of the plants from deer. (Appleton, 2008) T. erecta emits a very strong odor from the secondary compound and is therefore deer-resistant. The marigold also has a long history of medicinal use; it is mentioned in many ancient herbals for use in the treatment of headaches, toothache, swellings, and for strengthening the heart. It also has a number of culinary purposes and the flowers were found in many kitchen recipes.

In the American Civil War and World War I, marigold was used to treat wounds and prevent wounds from becoming infected with toxins and bacteria. In eastern countries, marigolds are often used in making garlands frequently used in festivals. (URL 3, URL 4, 5)

The petals of marigold are used to make an eyewash and is also used in both homeopathic and conventional medicine as a healing ointment for cuts and grazes. Marigold has anti-septic, stimulant, and anti-fungal properties. (URL 3, URL2, 5)

Works Cited

Appleton, F. (2008). Deer in the Urban Landscape. Aggie Horticulture.

Falsetto, S. (2008). The Medicinal Uses of Marigold Flowers. Retrieved from:http://www.suite101.com/content/the-medicinal-uses-of-marigold-flowers-a84067 URL3)

Garden Guides. (2010). Marigold. http://www.gardenguides.com/92-marigold-garden-basicsflower-annual-tagetes-patula.html (URL 1)

Grieve, M. (1995). Marigold. Retrieved from:http://botanical.com/botanical/mgmh/m/marigo16.html (URL 5)

Lawless, Julia 2001 The Aromatherapy Garden UK: Kyle Cathie Ltd

Plant Cultures, Marigold—other uses. Retrieved from:http://www.plantcultures.org/plants/marigold_other_uses.html (URL 4)

Podlech, Dieter 2001 Herbs and Healing Plants of Britain and Europe UK: Harper Collins (Collins Nature Guides)

USDA (2010). Plants Profile: Aztec marigold. Retrieved from: http://plants.usda.gov/j ava/profile?symbol=TAER (URL 2)