Morphological Descriptors For Identification
Many characteristics are used to identify sugarcane varieties, but only by using all of them together can an accurate identification be made. Many features are not consistent but change with the environment, particularly sun exposure. This section covers a range of identification features, how to observe them, and common mistakes made.
In approaching a clump of sugarcane, the first thing to notice is the stature of the plant. Is the plant very erect, or does it prefer to lean outward? Are the stalks very straight, or do they like to curve? Do the shoots come out very close together, or does the clump like to spread? Is it tall and spindly, or short and stocky? These aspects of the growth habit can help in determining the cultivar. However, these features do vary! A well-spread clump may merely be an old planting that has ratooned many times, a leaning clump may have just been poorly planted, and a spindly clump may be the result of having grown in the shade. While the entire stature of the plant should be considered, the curvature of the stalks is the most telling feature. A very erect cane will not bend much, even if the stalks are leaning outwards; conversely, the stems of a recumbent cane will curve near the base even if the clump as a whole is very upright.
Also, observe the leaves from afar. In general, they may be stiff and erect, they may droop towards the middle of the blade, or they may droop just at the tips. They may also grow densely or more openly. The stature of the leaves is more consistent than the stalks but may be unreliable in windy areas, where even very erect leaves may appear drooped. Also look if there is any hint of color to the leaves. Often the reddish or bluish tinge is only apparent from the right distance as the sunlight reflects off the leaves, and this trait may be overlooked if observing the cane too closely.
Getting closer, the most noticeable feature will be the colors of the stalk. It may be tempting to identify a cane by the coloration alone, but this is not advisable. Different cultivars may be virtually identical in color. More importantly, a single cane variety will vary in coloration depending on soil conditions, moisture, sun exposure, age, and natural variability. Along the length of a single stalk, the colors will differ from the top to the bottom or where shade has been cast. Many factors other than sun exposure may also affect the appearance of the stalk. The best color observation is on mid-aged shoots near the top, just a few nodes below the last healthy leaf.
Finally, all sugarcanes are covered with wax to varying degrees. Often the Hawaiian sugarcanes have a sparse, shiny wax bloom, but others are so thickly coated with white wax as to obscure the color of the cane altogether. On old stalks, you will find that the wax has washed off, but even on young, healthy shoots there may be more or less wax. Because of the variability in the appearance of the stalks, the limitations must be recognized - the stalks are a useful feature to narrow down the possibilities but not sufficient to make an accurate identification.
Although we think of sugarcane stalks as being cylindrical, the internodes take several different shapes, from concave to extremely barreled. Each cultivar favors a particular form but will differ based on the growth of the plant. The shapes can be challenging to clarify on most stalks, especially when leaning. The differences are often subtle, but observation of many internodes does reveal a shape preference. To assess the shape, look at healthy, mature, erect shoots near the center of a clump. In cases where the stalk shape is exceptionally expressive, such as the highly barreled 'Hāpai' cane, it can be a useful giveaway to quickly identify or narrow down the variety.
Zooming in further, more detailed features along the stalks are noticeable. A significant feature of the internode is the bud furrow, a depression that starts behind the bud and extends upward. The groove may be non-existent (absent), shallow (inconspicuous), or deep (strongly marked), and may continue the whole length of the internode or stop partway up. Unlike most of the characteristics mentioned so far, the expression of the bud furrow is very consistent, except on very short-jointed stalks, in which case the groove tends to disappear on all varieties. A less noticeable feature are corky cracks – small fissures in the rind of the cane. This feature is typically absent on Hawaiian cultivars, and so their conspicuous presence usually indicates a non-Hawaiian variety. Finally, stalks may be more or less prone to producing large splits, known as growth cracks.
At the node, many morphological features occur. These elements include the leaf scar, wax band, root band, growth ring, and bud. At the center of the node is the leaf scar, a lipped protrusion where the leaves attach. The leaf scar may be either straight or inclined, and while each variety favors one or the other, it is a variable feature. For kō, the most valuable observation is to note if hairs are protruding outward, which immediately indicates one of two kō varieties. Directly below the leaf scar is the wax band. The wax band will be indistinguishable from the bloom on a heavily waxy cultivar, but the dense ring of wax is clearly visible on most sugarcanes. While not particularly noticeable, the wax band ranges in width and may tend towards being tumescent (swollen) or depressed. Immediately above the leaf scar is the root band, where the root eyes, or primordia (earliest structural stage of the roots), are located. This section will consistently vary in height and shape. While often similar in color to the stalk, the root band is occasionally quite expressive in hue. Notably, for banded varieties, the stripes may extend through, truncate in, or stop short of the band. The number of primordia is variable, ranging from two sparse rows to six densely packed rows. While most cultivars have three or four rows of root eyes, the presence of only two or more than five rows is useful for identification. Along the upper edge of the root band is the growth ring. This narrow line is often distinctly colored, but with high sun exposure tends to be the same as the internode. Depending on the cultivar, the growth ring may be tumescent or not, and may curve to accommodate the bud.
The bud, located within the root band, exhibits a diversity of forms. These shapes may then be large or small, long or short, and flat or plump. The bud growth may extend above the growth ring or stop short of it. While all very young buds are green, flat, and flush against the stalk, at the proper stage of maturity, they exhibit a range of colors, sizes, and angles of projection from the stem. Along either edge of the bud is a membranaceous growth called the wings. The wings vary in color and width, but the trait most often noted is whether they start in the upper or lower half of the bud. Both the bud and the wings may be pubescent, and over 30 distinct hair groups are described along the front and back sides. In this guide, we focus only on a couple of the most prominent and noticeable hair groups that help in quick identification.
Moving further up the plant we reach the leaf and leaf sheath. The leaves themselves are not particularly revealing. The most noticeable trait will be any coloration or variegation present. The color may be strikingly apparent or just a slight tinge of color seen in the reflecting glare. Variegation occurs in many varieties, and is described by its intensity (how densely a single leaf is variegated), frequency (how many leaves are variegated), and color. The size of the leaves will vary considerably depending on the environment, but the length and width vary in concert. Therefore, the length to width ratio, called the leaf module, consistently falls within a small range for each variety and is a reliable characteristic.
The leaf sheath in more expressive than the leaves, and essential for identification. Some varieties are only distinguishable by the sheath! The sheaths show a broader range of colors than the leaves, often flushing with red or purple, and also express variegation much more strongly, typically with white, pink, or purple. The sheath's level of waxiness is another useful description, ranging from virtually wax free to heavily coated with wax. Less visually apparent, but fundamental for identification, is the pubescence; these are the irritating hairs that lodge in your skin when working with sugarcane. In some clones, the sheaths are entirely smooth, while in others they are densely pubescent. The hairs are concentrated into distinct areas, mainly down the middle and on the upper sides of the sheath. The hairs can be washed off in heavy rains or rubbed off in windy areas, so be careful when assessing pubescence. Other smaller characteristics of the sheath are how persistently it clings to the stalk and if the sheath cracks open to allow the emergence of the bud. In general, the prevalence and location of the hairs, and the color and intensity of the variegation are the most essential features of the sheath.
Where the leaf sheath meets the leaf, two critical identifying features are found: the dewlaps and the auricles. The dewlaps are the hinge of the blade joint that occurs at the juncture of the leaf and the sheath, and consist of two symmetrical patches (one on each side) that will differ in color and structure from either the sheath or the leaf. The dewlaps vary in color from yellow to dark purple, and in some varieties are ringed with bright pink or purple. There are four basic shapes – rectangular (called squarish), deltoid (triangular), double crescent (curved), and ligular (undulating, tongue-shaped). Descriptions of orientation, such as ascending or descending, and size, such as narrow or broad, are often added. Many intermediate forms exist and are recognized, but knowing the basic shapes can help considerably in identifying a specific variety. Dewlaps are best observed on fat stalks with large, healthy leaves. It is best to look at a moderately young blade, maybe stripping off a couple of older leaves first because the color will deepen over time to olive or olive-brown in many varieties.
The auricles are appendages on the leaf sheath, emerging from either side of the sheath just below the dewlap on the margin of dead leaf tissue. The auricles are usually asymmetrical and weakly developed, particularly with the Hawaiian canes, but well-developed auricles are a conspicuous feature and can be found within any mature clump with a probing search. The auricles take many shapes – from complete absence to long sharp protrusions. When the auricles are absent or transitional, a tuft of hair is often present that varies in length and density. When using the auricle for identification, remember that the two sides will differ, and so it is important to inspect them both. Also, remember that well-formed auricles are rare, so check many different stalks and leaves to find a well-developed example.
Finally, the cross-section of a sugarcane stalk allows the observation of the flesh, which varies in color from white to dark brown, and the rind. Some cultivars have a green, yellow, or orange tinge to the flesh, while others transition from being very dark near the skin to perfectly white at the core. In some varieties, distinct radial fibers are present.
Identifying Hawaiian Sugarcanes
The Hawaiian cane varieties are distinctly different than most other cane varieties around the world. Of the important island centers of sugarcane diversity, including Papua New Guinea, Hawai‘i, Java, and New Caledonia, the Hawaiian canes are considered the most homogeneous. This means they are simultaneously relatively easy to distinguish from foreign cultivars and challenging to tell apart from one another. One outstanding and consistent feature of Hawaiian varieties is a long, sloping transitional auricle that often consists of a poorly developed nub occurring an inch or more below the dewlap. The opposite auricle is typically heavily fringed with hairs, often with the fringe descending beyond the insertion point of the auricle. Therefore, any canes with well-developed pointed auricles, or having both inner and outer auricle developed, are most likely not native Hawaiian cultivars. In general, kō varieties have minimal stalk wax and strongly marked bud furrows, but these are only generalizations and not necessarily indicative. All the other features of appearance, pubescence, stature, and so on are highly variable.
Some Notes On Naming
Sorting through the cane names is difficult, with contradicting information. Here are some of the reasons why:
- Before European contact, the same variety of kō was often known by different names in different locales. Conversely, the same name was occasionally applied to separate sugarcanes.
- With new cultures, practices, and varieties arriving with Europeans, more names arose. Introduced canes were often given Hawaiian names, and sometimes native cultivars were given English names.
- As germplasms were established, sometimes no traditional name was recorded, and so new, generic names were created. Often these were place names, which adds a layer of confusion because many traditional names also utilize place names.
- To simplify management, codes such as H.O. (Hawaiian Officinarum) and H.C. (Hawaiian Cane) were applied to unknown varieties, which appear to have been applied to both native and introduced cultivars.
- Over time, collections became mixed up within the plots, which is easy enough to do. When germplasms were shared or copied, these naming errors propagated through the different users.
- The canes mutate into different varieties, and these changes can be propagated if care is not taken.
- When naming mistakes are noticed in the collections, the variety is often renamed with 'Not.' For instance, a cane held as 'Ko Kea,' was deemed to be incorrect and renamed to 'Not Koea.'
- Reestablishing the correct name to the correct cane, often based on conflicting historical information, is not a straightforward process.
This guide does not mean to tell anyone that the name they use is incorrect. This guide attempts to create a standard for communication so that when we talk with others and say a name, we can be sure that we are talking about the same cane. The research has used a wide range of modern and historical sources of information and thousands of detailed observations of sugarcane varieties to triangulate the most popular name for each variety, which is presented as the primary name. Any synonyms identified are given, along with a cross-reference of all the names found.
Authored by: Noa Kekuewa Lincoln.
Please properly cite any use of information or graphics from this page.
Lincoln, N. (2017) Description of Hawaiian Sugarcane Varieties.
Retrieved from: http://cms.ctahr.hawaii.edu/cane