Evaluation of a Selection of South African Plectranthus Species as Indoor Plants

Ryan J. Cheng and Professor Marilyn DalyDepartment of Biological Sciences, York College of Pennsylvania

• South Africa is renowned for its plant biological diversity and many South African plants have been cultivated through the centuries. Plectranthus verticillatus, the common “Swedish Ivy” houseplant, was the first species of Plectranthus brought to and popularized in the United States in 1960. However, most of the 53 South African Plectranthus species are relatively unknown in cultivation (Jaarsveld 2006).

• Plectranthus species have a variety of growth habits ranging from upright and shrubby bushes to sprawling ground covers. These habits suggest how Plectranthus can be used in cultivation—in hanging baskets, cascading over the edges of pots, or growing upright in containers.

•Most Plectranthus are shade-tolerant, forest floor species while some species are succulent and semi-drought tolerant and thrive in full sun. Plectranthus are easy to propagate from seeds and cuttings (Brits 2001) and require very little care. These qualities characterize qualites of successful house plants.

• Plants must be objectively evaluated prior to being promoted commercially for garden or indoor use. Plant trials provide an objective mechanism to evaluate a plant’s performance. Important performance criteria for indoor plants are: vigor, foliage interests, resistance to disease and pests, and habit. Flowers, although not necessary, are an added attraction.

• This project evaluated 28 South African Plectranthus species and cultivars from South African and North American sources. The plant trial was conducted in the York College of Pennsylvania greenhouse from September 21, 2008 to January 10, 2009.

INTRODUCTION

RESULTSMETHODS

EVALUATIONS

DISCUSSION

• Brits, G.J., Selchau, J. and van Deuren, G. 2001. Indigenous Plectranthus (Lamiaceae) From South Africa as New Flowering Pot Plants. Acta Hort. 552:165-170.

• Jaarsveld, E. 2006. The South African Plectranthus. 1st ed. Fernwood Press, Simon’s Town, South Africa.

LITERATURE CITED

ACKNOWLEDGEMENTS

I would like to thank Professor Marilyn Daly for her endless guidance, insight, and support for planning and completing this project. I would also like to thank Dr. Richard Daly and the YCP Biology department for their help and support of this project. I am also extend thanks to Huntington Botanical Garden, Kirstenbosch National Botanical Garden, New Plant Nursery, and RKS Greenhouses for supplying plant material for this project.

OBJECTIVEThe objective of this project was to describe and evaluate the performance and horticultural qualities of 28 South African Plectranthus.

CONCLUSIONS1. When choosing a Plectranthus for a house plant, one

should consider its natural habit and habitat and select a plant for its specific horticultural qualities.

2. Growers and consumers should obtain plants from reliable sources and be aware that there can be discrepancies in nomenclature.

FORMULAS:

[(.30 x Vigor) + (.20 x Resistance)] = Health Qualities

[(.40 x Foliage Interest) + (.05 x Habit) + (.05 Flower)] = Horticultural Interest

(Health Qualities + Horticultural Interest) = Overall Season Score

Species: Health: Interest: Overall:P. fruticosus 'James'1 2.13 2.25 4.38P. fruticosus 'James'2 2.05 2.25 4.30P. verticillatus 'Barberton'3 2.49 1.80 4.29P. verticillatus2 2.48 1.80 4.28P. 'Mona Lavender'4 2.30 1.85 4.15P. neochilus3 2.50 1.65 4.15P. neochilus2 2.48 1.65 4.13P. ecklonii 'Tommy White'2 2.09 2.00 4.09P. 'Cape Angel Edelbau'2 2.44 1.65 4.09P. ecklonii 'Medley Wood'2 2.06 2.00 4.06

Table 1. Top 10 – Overall Season Performance Table 1.

These are the 10 top performers that earned above average scores of >4 out of a possible 5 points for overall season performance.• 7 of the top 10 performers were cultivated varieties. *This would be expected since cultivated varieties have been carefully selected for their horticultural qualities.• 3 of the top 10 performers were straight species. *These results suggests that while cultivated varieties of Plectranthus have superior horticultural qualities that make them excellent house plants, there are also species plants that should also be considered as viable indoor plants.

Figures 3, 4, 5.

These are duplicate cultivars of P. fruticosus ‘James’ from two sources—one in SA and one in the US. • Both scored equally well, thus one might conclude that this confirms the

horticultural value of this cultivar. • However, even though they were supposed to be the same cultivar and their

performance scores were equal, their foliage color and size of the plants differed between plants from the two sources.

• P. fruticosus ‘James’ from New Plant Nursery displayed yellow-green foliage and a shorter size compared to the P. fruticosus ‘James’ from Huntington Botanical Garden which exhibited a dark-green foliage and a taller stature.

*These observations suggest that these two plants are not the same cultivated variety, but both have very good horticultural qualities.

Figures 6, 7.

This compares the straight species P. verticillatus to the cultivated variety P. verticillatus ‘Barberton’. • Both samples had almost identical scores in all categories each week and in their

overall season performances.• Their habits, foliage, and flowers looked identical to each other.*These results question whether ‘Barberton’ is a unique cultivar or if this sample was indeed ‘Barberton’.

Figures 8, 9.

P. ‘Mona Lavender’, P. ‘Cape Angel Edelblau’, and P. ‘Cape Angel Dark Pink’ are crosses between P. hillardiae X saccatus (Brits 2001, Jaarsveld 2006). • Both P.‘Monal Lavender’ and P. ‘Cape Angel Edelblau’ performed very well. P.

‘Mona Lavender’ obtained a higher Interest score due to its longer period of flowering. P. ‘Cape Angel Edelblau’ achieved a higher Health score due to its higher resistance to diseases and pest.

• P. ‘Cape Angel Dark Pink’ was not among the top performers. It achieved an interest score which was very similar to the other two related cultivars, but its health score was low because it was not as vigorous as the other two.

*These results suggest that there are important performance differences between related cultivated varieties and therefore one should make selections carefully.

USDA Plant Permit

Received Cuttings From U.S. and S.A. Sources

Maintained and Evaluated inYCP Greenhouse

Planted in soil-less mix in progressively larger containers:

2.5 x 2.5 trays

7.6 cm pots

15.2 cm pots

Health Qualities

Vigor30%

Resistance to disease and pests

20%

Total Health Score50%

Horticultural Interest

Foliage Interest

40%

Habit5%

Flower 5%

Total Horticultural Interest Score50%

Conducted weekly evaluations from:September 2008 January 2009

Evaluation Criteria and Percent Value

Defined evaluation criteria and assigned point values for each level of performance

1cuttings were obtained from Huntington Botanical Garden, California2cuttings were obtained from New Plant Nursery, South Africa3cuttings were obtained from Kirstenbosch Botanical Garden, South Africa4cuttings were obtained from RKS Nursery, Pennsylvania

Figure 1. P. ‘Mona Lavender’ in YCP greenhouse.

Figure 2. YCP greenhouse with P. ecklonii in foreground.

Figure 3. Comparison of P. fruticosus ‘James’ from Huntington Botanical Garden , California and New Plant Nursery, South Africa.

Figure 5. P. fruticosus ‘James’ from New Plant. Nursery.

Figure 4. P. fruticosus ‘James’ from Huntington Botanical Garden.

Figure 7. P. verticillatus and P. verticillatus‘Barberton’.

Figure 9. P. ‘Cape Angel Edelblau’

Figure 10. P. ‘Cape Angel Dark Pink’.

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reFigure 6. Comparison of the species P. verticillatus with the cultivated form P. verticillatus ‘Barberton’.

Figure 8. Comparison of 3 cultivated varieties bred From crosses between P. hilliardie x saccatus.

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