Hostas are tough herbaceous plants that grow perennially and develop into clumps. These plants emerge from small, occasionally stoloniferous (bearing stolons or creeping roots) rhizomes having plump white-hued roots. More often than not, the leaves of hostas appear at the base of the stems, are stalked, big and uncomplicated, usually developing into a mound. Hostas bear large, tube or funnel-shaped flowers, generally having six radial lobes that are either white or deep purple. The stamens are curved, reclining on the tube and appear in a raceme or simple inflorescence above a scape, which is generally unbranched.
Nearly all varieties of hostas mature to form dome-shaped mounds; a typical example of this is H. sieboldiana “Elegans”. However, a number of hostas form a low, instead of compressed mounds, for instance, H. “Resonance”. There are other varieties of hostas that are distinctly erect and the petioles of these plants are noticeably visible when one looks at the plant, as in the case of H. “Krossa Regal” or H. nigrescens.
Hostas with stolons (also known as stoloniferous hostas) usually form colonies of intertwined individual plants. As a whole, the colony may look to be flat, but the individual plants in the colony will still have a dome-shape or they will be erect or flattened.
The leaves of hosta can also differ in their overall contour – especially the form of the leaf’s base and the tip. In general, the shape of the leaf is described with regards to the ratio between its length and width. On average, the ratio of an oval-shaped leaf may either be 2:1 or 3:2. The length and breadth ratio of a broad oval shape is 6:5, but in case the leaf is extra wide, its ratio will change to 1:1. In such cases, the shape of the leaf is described as being round. There are other extremes too. For instance, a hosta leaf may be narrowly oval having a length and breadth ratio of 3:1. When the leaf becomes further narrow, its shape is described as lance-shaped or elliptical and has a ratio of 6:1.
The leaf bases found in different varieties of hostas are of four types – heart-shaped (leaves having two identical, rounded lobes on either side of the petiole or stalk at the point where it goes into the leaf blade); wedge-shaped (leaves having straight sides, but are converging); truncate (the leaves appear as if they have been slashed directly through their base); and attenuate (leaves whose sides are arched and converging). While these classifications of the hostas leaf bases are not fixed, they usually flow from one category to another. Therefore, in reality, one will not find the hostas leaf bases to be heart-shaped, or truncate, but it will be something in between.
Similarly, the tip of hostas leaves may either be cuspidate (get thinner gradually and ending at a sharp point), or mucronate (suddenly ending in a sharp point). Tips of some leaves of this genus may also be obtuse (rounded) or acute (converging in a point).
Juvenile and Adult Leaves
Several varieties of hostas undergo two phases during their existence – juvenile phase and adult phase. The leaves produced by the plant during the juvenile phase are usually narrow compared to those produced during the latter phase. This can especially be noticed in plants that have been tissue-cultured. In fact, the spring leaves of several hostas differ from the leaves they produce during the summer. The leaves that are produced more recently are in the middle of the clump. In addition, some varieties of hostas have a characteristic late flush of leaves, for instance, the leaves of H. “August Moon”. These leaves are longer as well as smooth, while the main leaves of the plant are coarse and creased. The H. “Undulata” produces the second flush of leaves that have a mottled green appearance instead of the crispy multicolored look.
Leaf Substance and Margins
The thickness or substance of hosta leaves may differ significantly. In fact, this aspect is a key issue in determining the degree to which snails and slugs will consume them. The breadth or slenderness of the leaves is only stated when the leaves significantly depart from the standard.
The hosta leaf margins are never broken, but always entire. In other words, the leaf margin is never cut, jagged, lobed or serrated. However, the margins of hosta leaves may differ in a number of other ways. They are flat in the case of H. “Devon Green” or somewhat rippled like in the case of H. “Daybreak”. On the other hand, the margin of the leaves of the species called H. pycnophylla may also be intensely wavy goffered, or crusty.
Leaf Plane, Surface, and Veining
The leaf of hostas may be twisted or undulating with deviations that have a propensity to go along with the wavy margin. Sometimes, the leaves may also be cupped, like in the case of H. “Tokudama”. On the other hand, the leaves of H. “Brim Cup” are convex, or somewhat arched as in the case of H. “Silver Lance”.
The surface of hostas blade may be dimpled (puckered) or smooth and the puckering might even be minor or deep, as is often seen on the leaves of full-grown plants. However, the leaves of juvenile plants are never puckered.
The leaves of hostas display a characteristic pattern of veins, known as campylodrome, which denotes that the veins enter the leaves at their base and arc away from the point as the leaves become wider and subsequently, again curve inwards as the leaves become slender near their tip. When you look at the leaves from above, the veins seem to be susceptible, but they appear to be conspicuous when seen from beneath. The veins appear to be corrugated or furrowed in places where they are intensely impressed. This is common in the hosta species H. “Green Acres”.
At all times, the leaves of hostas are smooth. In other words, they do not have any hair, but maybe discernible in different other ways. As in the case of H. yingeri, the leaves may be glossy or lusterless, but they are usually satiny. The leaves may also be coated with a waxy covering and this is always the case with blue hostas. In fact, the bluish tinge of these plants is attributed to this waxy coating. In some cases, the leaves may be pruinose or frosted and appear as if they are sheathed with chalk or frost. Usually, these effects are very prominent in young hostas’ leaves and they become lighter as the season draws closer. The effects also fade if the hostas are grown in extreme sunlight.
The various colors of the leaves of different plants are attributed to plastids – pigments contained by them and carried throughout their bodies. The prevailing plastids present all over the plant kingdom are green and are known as chloroplasts. These chemical structures are basically responsible for absorbing energy from the sunlight and transforming it into chemical energy. In other words, they work to convert light energy into chemical energy, which activates the metabolism of the plants. The leaves of different plants also enclose other colors, which are also attributed to pigments, which are transported by different plastids. It is significant to note that all the plastids present in the hostas leaves are incredibly identical. It takes only a few atoms to slip from one hue to another. In fact, such modifications can and do occur, although occasionally, when the cells replicate themselves.
These plastids are not constituents of the plant cell nucleus, but they are found in the areas encircling the nucleus. In other words, the plastids do not have any role in deciding on the form of the plant or any of its part, but just its color. In addition, the plastids are also quite apart from the nucleus and they also have their individual DNA – the indispensable programming code in cells of organisms that instruct them how they should copy themselves. Nevertheless, the cell replication is not akin to any contemporary factory line, wherein all the items at the end are similar. Sometimes there are errors while replicating and the truth is that such errors occur all over the natural world. In addition, the chances of errors enhance as the time passes. Therefore, the more mature a plant is, the chances of occurrence of such errors are greater. However, whether or not this kind of error will lead to a noteworthy new color combination actually depends on the place where the error takes place in a growing plant – the shoot or any other place.
It is worth mentioning here that the developing tips of any plant are necessarily the same all the times – irrespective of whether it is a new shoot or an embryo. However, any plant’s different parts grow from different areas of the growing tip. There are three different areas or parts of a growing tip – L 1, L 2 and L 3, which give rise to different parts of a plant. The external layer of the growing tip is the part which gives rise to the surface (called epidermis) of the leaf and this part of the growing tip has a vital role in deciding on the leaf margin. In case, colored plastids are present in the part called L 1, it is possible that the leaf will also have a colored margin.
The second or middle layer of the growing tip of a plant, known as L 2, has a more vital role and the larger part of the leaf develops from here. If this layer comprises colored plastids, it is likely that the center of the leaf will also be colored. Nevertheless, the fact remains that the plastids possess the aptitude to shift from one layer to another. For instance, plastids having their origin in the middle layer (L 2) may move to the first layer (L 1). This is exactly what happens when the stripes present in a streaked hosta drift to the leaf margin of the plant.
Moreover, the plastids may also lose their hue. As the laws of chance in nature enable the plastids to transform their color, there are means to rectify such errors. When such an error is rectified via different mechanisms, the plant or its leaf is supposed to “revert”. Apart from green, all other coloring and variegation are basically unsteady. However, it has been found that usually the marginal variegation’s (multicolored leaf margins) are more stable compared to the central variegation’s (multicolored leaf center).
The blooms of hostas appear on extended stems or scapes, which grow straight from the leaf mounds at the level of the ground and end in a somewhat crowded raceme (a simple intermediate inflorescence). The scapes of hostas are generally round in shape, which may either be straight or sometimes hollow. They are usually simple but sometimes branched, as in the case of H. tibae. The scape may also be straight, resting or curved. The blooms are positioned away from the scape on small pedicels, which bear the flowers in a slanting or horizontal plane. All the pedicels arise from a small bract, which is called the flower bract and holds onto the stem. These pedicels are often so petite that they are hardly noticeable when seen with the naked eyes, for instance, in H. sieboldii. On the other hand, they are sufficiently large and somewhat obvious like in the case of H. “Summer Fragrance”. A lot of times, the flower bracts dry up after flowering. In some hostas species as well as cultivars, the flower bracts turn out to be so big that they resemble leaves. Occasionally, they also envelope the flower buds, like in the instance of H. kikutii.
However, scapes may also produce another form of bract known as a foliaceous or leafy bract, which is often difficult to tell apart from that bract of a flower. The leafy or foliaceous bracts are found just under the scape’s flowering part. The size of these leafy bracts is largest closest to the ground. In most cases, these bracts are out-facing, but you will also find a number of small leafy bracts that hold on to the scape – a perfect example of this is found in H. “Opipara”. The leafy bracts of many hostas species as well as hybrids are prominent, as in the case of H. “Undulata”. Plants producing variegated (multicolored) leaves will generally have variegated bracts too.
Hostas bear flowers that are generally funnel-shaped or bell-shaped having about six spreading lobes as well as six stamens. The stamens are located just under the base of the ovary or are appended to the tube. Generally, the stamens are longer compared to the perianth and, hence, they appear to be protruding. The ovary of hostas flowers does not have any stalk. It comprises three cells and usually, the stigma also sticks out further than the stamens.
As far as the descriptive aspect is concerned, the middle section of the flowers is the most important. This part lies just between the lobes and the tube and it is responsible for the shape of the flower. In fact, a flower is bell-shaped or funnel-shaped depending on the expansion of this part of the flower. When this part enlarges irregularly going further than the tube, the flower will be bell-shaped. On the other hand, a flower is funnel-shaped when the tube stretches out slowly and the lobes to form a solitary unbroken curve. It is interesting to note that the blooms of a number of hostas varieties are double, and in some instances, the plants bear flowers which actually do not open ever – as in the case of H. clausa. Other hostas varieties, such as the H. yingeri and H. laevigata, produce flowers having slender lobes and can be described as being spider-shaped.
From the diagnostic point of view, the anthers of hosta flowers are important. The anthers of true hosta species either have a yellow or purple color, while those of hybrid varieties are generally bi-colored. However, the color of the anther can only be ascertained just prior to the shedding of the pollen.
The color of hostas flowers varies from somewhat deep purple to what seems to be chaste white. However, the lobes of a few hostas species, such as the H. plantaginea, may continue to retain a tinge of violet.
Initially, it was believed that only the hostas species known as H. plantaginea was aromatic. Hence, all the cultivars of this species that have been bred in the West owe their aroma to H. plantaginea. Nevertheless, recently botanists have discovered that cultivators in Japan grow a few aromatic cultivars, which were possibly not bred from H. plantaginea or have nothing to do with this hosta species.
Once the flowering is over, the ovary of hostas distends to form an extended, multi-chambered capsule. These capsules have the same color as the plant’s leaves. They are green in the case of plants bearing green leaves, while the glaucous (pale bluish-green) varieties produce glaucous capsules. Sometimes, the capsules also have a purple hue, as in the case of H. “Grand Master”. Similarly, variegated (multicolored) hosta varieties produce variegated capsules.
It takes about six weeks for these capsules to open after the flowering. The capsules contain seeds that are oval shaped and almost flat. If the color of the seeds is black, it means they are fertile. On the other hand, pale colored or almost white seeds are infertile and do not germinate. Therefore, even if a plant produces capsules, it does not mean that the seeds enclosed by them would be fertile. In fact, several hostas cultivars do not produce capsules. In such cases, the scapes wither after the flowering season.