Rhapis excelsa

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Figure 1. R. excelsa

Rhapis excelsa is a multi-stemmed dioecious (Ed: or hermaphroditic depending on seed grown variety) palm that grows to a maximum height of between 3 and 4 metres, each stem or cane is slender ranging from 10-30mm in diameter, depending on growing conditions and variety. The canes are usually covered by a coarse matted fibrous material which is actually the outer base of each leaf sheath. In Rhapis excelsa this leaf sheath fibre tends to be loose and rather ragged looking. The leaf sheaths are fairly persistent but when they do fall a dark green conspicuously ringed stem of leaf base scars is exposed: very similar in appearance to bamboo canes, hence the other common name bamboo palm. Individual canes can be closely ringed, or rings may be moderately spaced, depending on growing conditions.

In ideal growing conditions leaves are palmate, deep glossy green thick textured and divided into regular fairly broad segments usually to near the junction with the petiole but not always so. Mature palms which I have observed have from five to twelve segments per leaf with rather raggedly toothed ends of each segment. Segments are conspicuously ribbed and outer and inner segment margins are minutely toothed. Petiole is slender, often covered with a fine grey or brownish grey fluffy hair. The leaf blade may be up to 80 centimetres across, arranged in a semi-circle just greater than 180°. The petiole or leaf stalk may be up to 60 centimetres long although it is usually shorter. The leaf sheath may be up to 60 centimetres long, the edges of which are composed of brown or grey brown fibres.

Figure 1. R. excelsa (on left) next to R. humilis in Naples Botanic Gardens.

Inflorescences emerge from between the leaf sheath and stem and usually arise from the uppermost portion of the stem. On emerging the inflorescence has a pale pinkish tinge and is enclosed in pale green tubular bracts. As the inflorescence matures the bracts dry up and become brown and papery in texture. In my offset grown plants the inflorescence is branched to second order on female plants and to third order on male plants and, as most of my plants are to third order, I seem to have a predominance of male plants. Inflorescences are relatively short, brittle or stiff and tend to droop, flowers are arranged spirally on the second and third order branchlets and male flowers have a three lobed fleshy calyx, fused at the base. Male flowers have three petals which are fleshy and fused at the base and have six stamens and three small aborted fused pistils. Female flowers are similar but are not as elongated, the stamens are minute and there is a prominent three part pistil. Ripe fruits are white to cream, rounded and approximately 36mm across.

One of the reasons for this palm's popularity is its ease of culture. Rhapis excelsa is very adaptable to soil types although neutral to slightly acid soils with good drainage and organic matter is recommended for best results. This palm as is the case with most Rhapis species is an understorey plant so for best results a partially shaded spot under trees or a pergola is ideal. Rhapis excelsa can be grown in full sun as long as soils are good and adequate water is available. Leaves however will lose their deep green colouring, will become yellowish green and on the hotter days will probably burn. Temperatures as low as -5° C are tolerated by R. excelsa as it is quite cold hardy, particularly when grown under shelter, and it also grows in climates where it may be exposed to prolonged periods of cold weather. Very hot weather, particularly when the air is very dry, may cause damage which can be prevented by adequate watering, mulching and growing under other plants or pergolas and occasional hosing of foliage with a fine spray or mist can also help to maintain a higher relative humidity.

Figure 3. R. excelsa inflorescence.

As an indoor plant Rhapis excelsa has no palm rival. (Not even Howea forsteriana. ) Its ability to handle low light intensities, low humidity, varying temperatures plus its suitability to pot culture, small to moderate size and slow growth rate make this palm ideal for indoor culture. Rhapis excelsa has very few pests or diseases to trouble it. The only major pests are scale and mealybug. Scale can be easily controlled by physical removal, wash off with high pressure jet of water, or scrape off with cotton wool buds, or by chemical control with White Oil, or a systemic insecticide such as Rogor or Metasystox. Mealybug can be removed physically but it usually requires chemical control. For total control use a systemic insecticide and apply as a soil drench as mealybug often invades the roots of a plant, However, pest disease problems are few. The only problems I have had being root rot caused by fungus attack because of poor cultural practices and brown or black fungal spot on the leaves, usually symptomatic of poor nutritional status.

Root rots can be avoided through proper cultural practices such as choosing healthy plants in the first place and watering only when necessary. Provide good drainage so that water does not build up and stay around the roots of your plants. This means plant in raised beds when planting into poorly drained ground, or opening up the soil by adding organic matter or coarse sand or, in pots or tubs use potting mixes that conform to the Australian Standard. Poor drainage is the single most common reason for root rot in potted plants and, with stale water continually surrounding roots a low oxygen environment develops which is ideal for root rot to take hold.

But if, despite great care, root rot symptoms do develop, such as wilting, excessive browning of leaf tips and loss of vigour, firstly remove the plant from the soil it is in, wash roots bare of soil, inspect roots for fungus problems, remove black roots or reddish brown roots and replant into a raised bed of well drained soils. In the case of tub or potted plants do the same but plant into a clean well drained potting mix and, finally, drench the soil with a systemic fungicide such as Fongarid or Terazol or similar. Brown or black fungal spot is usually caused by poor cultural practices. To prevent the disease, buy only good quality plants and don't crowd plants too much so as to allow unimpeded air flow to reduce conditions ideal for the fungus. If leaf spot does occur remove and burn the affected leaves. Thin out plants or space potted plants to improve ventilation and finally spray all affected plants with a preventative fungicide such as Benlate or Mancozeb.

Figure 4. R. excelsa spectacular inflorescence.

For best results water only when the first few centimetres of soil or potting mix are dry and then water thoroughly so that there are no dry areas around the plant roots. In well drained soils and mixes this should result in a good balance of water and air. The large amounts of water leach out accumulated salts, toxins and carry oxygen to the roots. The better the quality of water applied the better your plants will grow in the long run, particularly plants grown in containers. Plants held indoors benefit by being taken outside when it is raining or being placed under a sprinkler for a period of time. Brown leaftips are often caused by an excessive accumulation of fertiliser salts in the potting mix. Thorough leaching will overcome this problem.

Contributed by:

Heinz-Dieter Froehlingsdorf (Text) (from Palms & Cycads No 39. Apr-Jun 1993).
Angelo Porcelli (Figure 2).
Ray Hernandez (Figure 4).
Ian Edwards (Figure 1&3)

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