Our Native Impatiens Species

Jewel-weeds

North Carolina has two native species of Impatiens, I. pallida, and I. capensis, more commonly known as Jewel-weed or Touch-me-nots.  Both species are found in rich, moist habitats ranging from cove forests, seeps, bogs, stream banks, and wet roadside banks and ditches. In the mountains they are a common sight along the Blue Ridge Parkway and many country roads. 

Impatiens pallida is commonly called Pale or Yellow Jewel-weed, or Yellow Touch-me-not. It is commonly found in the N.C. mountains and is a rare occurrence in a few piedmont counties. The plants bloom from July through September. According to Radford, Ahles, and Bell¹ they prefer a more neutral soil.  I also tend to associate Yellow Jewel-weed with richer more diverse habitats and higher elevations than Spotted Jewel-weed. The color of the flower can range from a dark to pale yellow to a cream, almost white, color with scarlet spotting in the throat (Figures 1, 2, 3, 4, 5). The cream colored flowers are unusual and I only know of a few areas where they grow. Many botanists often refer to this color variation as Impatiens pallida forma speciosa ² . I have seen all three color variants within a single population of plants. However, each individual plant had only one color form of the flower. Therefore, the color variation must be genetically based and not a product of environmental differences.

Figure 1:  Impatiens pallida, Yellow -Touch-me-not,
with bright yellow colorization.

Figure 2: This Yellow-Touch-me-not has a paler yellow color.

Figure 3: This is Impatiens pallida forma speciosa 
showing the cream to almost white color form.

Figure 4: In this photo I purposely posed a typical yellow
flower next to the cream colored variation for  better contrast.

Figure 5: Another example of the unusual color
form, Impatiens pallida forma speciosa. 

Impatiens capensis is commonly known as Spotted Jewel-weed or Orange Jewel-weed.  It is a common and fairly ubiquitous plant found across the state blooming from late spring into late fall. The bright orange flowers are often heavily mottled with darker orange spots (Figures 6, 7, 10, 11). The flowers of Orange Jewel-weed are smaller, longer, and more narrow than those of Yellow Jewel-weed. Impatiens capensis has an overall more relaxed or droopy appearance than I. pallida due to its longer leaf petioles.  These differences are easy to see in areas where both species grow together. Apparently, I. capensis also has some rare color variations ranging from an almost red form to a white form ^{1, 3}. During my many years of botanizing I have not come across either of these color variations. I would love to hear from my readers if they have!

Figure 6: Impatiens capensis, Orange Jewel-weed showing
the typical pale orange colorization with darker orange spotting.

Figure 7: Orange Jewel-weed, note the long reflexed nectary spur.

Vegetatively both species are very similar in appearance. They have alternate, elliptic to ovate simple leaves, with crenate to serrate margins (Figure 7). Plants can potentially grow up to two meters in height but are usually shorter (1-1.5 meters). The glabrous weak stems are hollow and succulent (Figure 8).

Figure 7: A leaf from Impatiens pallida, Yellow Touch-me-not.

Figure 8: The stems of Impatiens are hollow and succulent.

Since a child I have always been told that the mucilaginous sap soothes skin irritations such as poison ivy, sun burn, and pain from stinging nettles. You simply grab some stems, crush them, and rub the slimy juice onto the affected area for relief. When I am hiking I also use the juice as a preventative measure to reduce my chances of developing a rash after accidental contact with poison ivy. The internet is filled with personal testimonies touting the effectiveness of this home remedy. There is also a plethora of websites advertising the benefits of jewel-weed extracts, poultices, and salves. But very few formal scientific studies have been done to test the efficacy of Jewel-weed sap as a treatment for poison-ivy. One study I read concluded, “Jewelweed mash was effective in reducing poison ivy dermatitis, supporting ethnobotanical use.” ⁴ I now feel that my early mountain lore education has been validated. 

The zygomorphic flowers of the two species are similar in morphology. There are five stamens surrounding a single pistol composed of five fused (connate) carpels and five stigmas. The calyx is unique consisting only of three sepals in an otherwise pentamerous flower. One sepal is enlarged, brightly colored like the petals, and sac-like eventually tapering into a nectary spur. In I. pallida, Yellow Jewel-weed, the nectary spur (4-6mm)³ tends to bend downward at a ninety degree angle (Figure 9). In I. capensis, Orange Jewel-weed, the spur (7-10mm)³ is usually reflexed and parallel to the corolla (Figures 5, 9). The other two sepals are pale and much smaller, situated above and behind the upper lip (Figure 10, 11). The corolla is comprised of five petals. One petal forms a large upper lip, two smaller petals form the lateral sides, and the remaining two petals form a large clefted bottom lip that is often used as a landing platform for pollinators (Figure 12)⁵. Impatiens also have a mix of chasmogamous and cleistogamous flowers. Chasmogamous flowers open and are available to pollinators while the smaller cleistogamous flowers never open and are self-pollinated.

Figure 9:  Impatiens pallida, Yellow Touch-me-not, with a shorter, wider
and larger flower than Impatiens capensis. Also, note the shorter nectary
spur that bends downward at a 90 degree angle from the corolla.

Figure 10: Impatiens capensis, Orange Jewel-weed, with a
longer slimmer flower compared to I. pallida. Also, note
the longer reflexed nectary spur parallel to the corolla. 

Figure 11: Another Impatiens capensis flower showing the reflexed
nectary spur. Also, note that this flower has heavier spotting than
the previous flower (Figure 10) thus demonstrating some
of the natural variation within this species.

Figure 12: Typical flower morphology for Impatiens pallida and I. capensis.

Many species within the genus Impatiens are commonly called Touch-me-nots for an obvious reason; they have explosively dehiscent seed pods.  My Grandmother always had touch-me-nots, Impatiens balsamina, along her porch and as a child I would touch the ripened seed pods to watch them explode. Our two native species also have ballistic seed dispersal. The fruit is a five locular capsule. As the capsule matures internal tension builds up until the slightest touch triggers the seed pod to violently split open or dehisce.  As the five locular valves rapidly split apart and curl back, the seeds can be thrown up to a meter ⁶ in distance from the parent plant (Figures 13, 14, 15).

Figure 13: Developing seed pod of  Impatiens pallida.

Figure 14: View of capsule and seeds after explosive 
dehiscence. Note the coiled locular valves.

Figure 15: Sequential video tracings of an I. capensis seed pod before and during dehiscence. The numbers show the time in milliseconds from the start of dehiscence.⁶ (http://creativecommons.org/licenses/by-nc/2.0/uk/)

I have not found a satisfactory explanation for the common name of “Jewel-weed”. But I have several theories. I have noticed that early in the morning the plant’s leaves often exhibit a phenomenon called guttation. Guttation is a process that allows plants to release excess water from small glands along the leaf margins called hydathodes. This forms small droplets of water around the leaf edge that can glisten in the sun. Also, after photographing in a light rain, I noticed how the water beaded on the surface of the leaves and sparkled in the sunlight like small jewels (Figure 16)! But, no matter how they get their common name of "Jewel-weeds", they are one of my favorite wildflowers. Their delicately dangling and brightly colored flowers always catch my eye and I know it is truly summer when I see the Jewel-weeds in bloom! 

Figure 16: Rain droplets beading up on the
surface of  Yellow Touch-me-not leaves.

Notes: 

All photographs were taken by and are property of Tracie Jeffries unless otherwise noted.

Resources:

1. Radford, Albert Ernest, Harry E. Ahles, and Clyde Ritchie Bell. Manual of the Vascular Flora of the Carolinas. Chapel Hill, NC: University of North Carolina Press, 1983. Print.

2. Jennings, Otto E. “Impatiens Pallida Forma Speciosa F. Nov.”, The Ohio Journal of Science. V 20, Issue 6, April 1920, p 204, http://hdl.handle.net/1811/2089.

3. Weakley, Alan S. Flora of the Southern and Mid-Atlantic States. Chapel Hill, NC: U of North Carolina Herbarium, North Carolina Botanical Garden, University of North Carolina, Chapel Hill, 2015. Print.

4. Motz, Vicki Abrams, et al. “The effectiveness of jewelweed, Impatiens capensis, the related cultivar I. balsamina and the component, lawsone in preventing post poison ivy exposure contact dermatitis.” Journal of Ethnopharmacology, vol. 143, no. 1, 2012, pp. 314–318., doi:10.1016/j.jep.2012.06.038.

5. Caris, P. L., et al. “Floral development in three species of Impatiens (Balsaminaceae).” American Journal of Botany, vol. 93, no. 1, Jan. 2006, pp. 1–14., doi:10.3732/ajb.93.1.1.

6. Marika Hayashi, Kara L. Feilich, David J. Ellerby; The mechanics of explosive seed dispersal in orange jewelweed (Impatiens capensis), Journal of Experimental Botany, vol 60, Issue 7, 1 May 2009, pp. 2045–2053, https://doi.org/10.1093/jxb/erp070.