Rhododendron arborescens

Rhododendron arborescens, also known as smooth azalea[1] or sweet azalea, generally blooms in late spring and early summer. It is named sweet azalea after its sweet aroma. The flowers range in color from white to pink with red stamens. The glossy green leaves can also become deep red to purple in the fall. This plant, indigenous to the United States, is generally found growing near moist areas or streams.[2] The plant prefers growth in acidic soil with a pH of 6.8 or less. It grows best in sandy soils above 3000 feet. Grows to a Height of 8–10 feet.

Rhododendron arborescens
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Angiosperms
Clade:	Eudicots
Clade:	Asterids
Order:	Ericales
Family:	Ericaceae
Genus:	Rhododendron
Species:	R. arborescens
Binomial name
Rhododendron arborescens (Pursh) Torr.

The flowers are also known to contain poisonous substances and must not be consumed by wild animals or humans. The effects of consuming this plant include depression, vomiting, diarrhea, difficulty in breathing, and most dangerously coma.[3]

History

The official credit for the discovery of R. arborescens goes to Frederick Traugott Pursh and John Bartram. It was first observed in John Bartram's garden in Philadelphia as well as Blue Mountain, Pennsylvania.[2]

It has also been mentioned that the plant was initially noticed by André Michaux in 1795 in the state of North Carolina. However, after further investigation, no more species were found in his conservatory. Therefore, the recognition for the discovery of the plant was given to Frederick Traugott Pursh and John Bartram.[2]

Rhododendron arborescens was first named Azalea arborescens by Pursh in 1814. However, John Torrey renamed it Rhododendron arborescens in 1824 because he believed that it should not be taxonomically separated from the rhododendrons.[4]

Immature flowers of Rhododendron arborescens

Plant morphology

Rhododendron arborescens is a shrub up to 18 feet tall, with terminal inflorescences growing from the end of the stems. These plants also generally have yellowish-brown twigs. The leaves are oval and entire with round tips. The midribs of the leaves are known to be hairy. The leaf itself is green and waxy and approximately 1.75 to 3 inches long. It is also observed that plants that are found at higher altitudes generally have smaller leaves and smaller heights. The plant produces from 3 to 7 flowers after a white or blue shade has appeared on the leaves. These flowers contain red stigma which are quite visible all the way up to the petals. This plant is also known to be deciduous.[2]

Distribution

They are distributed in the eastern part of the United States. They are known to grow in parts of West Virginia, Pennsylvania, Tennessee, North Carolina, Georgia and Alabama. They are found among streams near mountains or moist forests. Rhododendron arborescens are generally known as late bloomers. They have a range of blooming from early April till September.[2]

Cultivation

R. arborescens grows best in soil that is slightly acidic at a pH of 5.5-6. It does not grow well in excessive water and drainage is necessary for healthy growth. It is tolerant of full sunlight but must not be overexposed. It is beneficial to plant it with the roots slightly above the ground and accumulating soil up to the plant roots. Organic matter such as sawdust and pinebark may aid the growth of the plant. Depositing a few inches of pine bark or wood chips may help in keeping moisture and preventing weeds from growing around the plant. However, mature R. arborescens do not need to be fed with fertilizer.[5]

This plant has gained the Royal Horticultural Society's Award of Garden Merit.[6][7]

Toxicity

Structure of Grayanotoxin

R. arborescens contains andromedotoxins, specifically known as grayanotoxins which are water-soluble diterpenoid compounds. Both the leaf and flowers of this plant are sources of toxins. Consuming as little as 3 milliliter of nectar per kilogram body weight may be highly pernicious.[8]

Mechanism

Andromedotoxins bind to the Na channels of cell membranes which increases the influx of sodium in the cell and causes extended depolarization. This causes sodium channels to accommodate calcium influx into the cell which also results in depolarization.

Cardiac Action Potential

Diagnosis

Leaf or flower consumption of R. arborescens results in drooling and a blazing sensation in the mouth. This is supplemented with emesis, diarrhea, muscular weakness and weak vision. Other lethal cardiovascular effects include bradycardia, hypotension, and atrioventricular block. Dyspnea, and prostration may develop and someone may die in the span of one to two days.

Possible Treatments

One way to possibly treat it is to detoxify the body. Emesis, or forcefully vomiting, is one way to rid the body of harmful compounds. Another way to treat it may be to replace the internal body fluid and receive respiratory support. Quinidine is an example of a Na channel blocker which may be helpful in curing heart block.[8]

Structure of Quinidine

References

1. "Rhododendron arborescens". Natural Resources Conservation Service PLANTS Database. USDA. Retrieved 21 October 2015.
2. Clark, Susan. "Species in our Midst".
3. "Native Plant Database". The University of Texas at Austin.
4. Bailey, L.H. (1963). How Plants Get Their Names. Macmillan Company.
5. "National Native Azalea Collection". The North Carolina Arboretum.
6. "Rhododendron arborescens". www.rhs.org. Royal Horticultural Society. Retrieved 24 February 2020.
7. "AGM Plants - Ornamental" (PDF). www.rhs.org. Royal Horticultural Society. July 2017. p. 107. Retrieved 18 February 2020.
8. Chan, Alexander. "Poisonous Plants". Archived from the original on 2012-03-17.