Botany 101: Flowers

Standard
20171205A Petr Kratochvil, PublicDomainePictures.net.jpg

This hibiscus is a typical single flower: five petals and clearly defined pistil and stamens in the center. Source: Petr Kratochvil, PublicDomainePictures.net

We probably all learned some basic botany back in school … and have almost certainly forgotten some of it. In a blog about gardening, therefore, it can’t hurt to do a bit of revision from time to time. So here is a bit of basic botany about flowers.

What Is a Flower?

20171205B Petr Dlouhý, Wikimedia Commons.png
The structure of a typical flower. 1. Receptacle. 2. Sepal. 3. Petal. 4. Stamens. 5. Pistil. Source: Petr Dlouhý, Wikimedia Commons

The flower is the reproductive structure of higher plants, the place where seeds, which will produce the next generation of the plant, are produced.

The flower is carried on a small stalk called a peduncle that joins a receptacle: the base of the flower.

The outer envelope of the flower, especially visible when the flower is in bud, is called the calyx. It generally consists of green, leaflike sepals, although they are sometimes colored. The flower sometimes has one or more colored leaves called bracts arising from its base. The poinsettia (Euphorbia pulcherrima), for example, is well known for its colorful bracts.

The inner envelope of the flower is called the corolla. It is often colored and is made up of petals.

Sometimes petals and sepals look much alike. This is the case with lilies, tulips and daylilies, for example. They’ll then be called tepals.

The Sex of Flowers

Most flowers are bisexual (hermaphrodites) and bear both male reproductive organs (stamens) and female reproductive organs (pistils).

 

20171205C ENG www.funscience.in.png

Structure of a stamen. Source: www.funscience.in

Stamens consist of a filament bearing an anther at its tip. The latter contains pollen sacs which are, as the name suggests, filled with pollen (male gametes). Pollen is usually carried from one flower to another by insects (less often by birds or mammals) or by the wind, more rarely by water (a few aquatic plants). There can be from one to over one thousand stamens per flower.

20171205D ENG www.funscience.in.jpg

Structure of a pistil. Source: http://www.funscience.in

The pistil (the female reproductive organ) is made up or one or more carpels. When it carries only one carpel, it’s said to a simple pistil, but a pistil can also be compound and have several carpels. The carpel is made up of three parts: a swollen base called the ovary, a narrow, tubelike style and, at the tip of the style, a stigma. The ovary can be simple or compound and contains the ovules that will become the seeds once pollinated. The stigma is knoblike and has a sticky surface. It serves to receive pollen grains.

Fertilization

20171205H ENG2.jpg

The pollen grain forms a pollen tube through which the sperm cells descend to fertilize the ovule. Source: laidbackgardener.blog

Once the pollen grain is deposited on the stigma, it emits a pollen tube that extends to the ovary and the sperm cells descends the tube to fertilize the egg. An embryo develops that turns into a seed. When the seed is mature and falls to the ground (or any other suitable surface), it sprouts and produces a new plant.

Sex Can Be Complicated

Most flowers (about 90% of them) are hermaphroditic: they house both sexes and are said to be perfect flowers. Other flowers are imperfect: they are entirely female or entirely male. Sometimes female flowers—those of the kiwi (Actinidia spp.) for example—have visible, but non-functional, stamens. The opposite is also possible: male flowers can have visible but non-functional carpels.

Some plants bear separate male and female flowers on the same plant. They’re called monoecious, from mono, for one. Squashes and cucumbers as well as begonias are monoecious.

If a plant is said to be dioecious, that means is it carries male and female flowers on two different plants. (Note the “di,” for two, in the name.) The plant that bears only female flowers is called gynoecious; the one that bears only male flowers is androecious. Remember when the nursery guy told you to plant at least one male holly to ensure your female hollies produce berries? That’s because hollies are dioecious. Willows, poplars and yews are other examples of dioecious plants.

The More the Prettier

Most flowers are single flowers. They bear the “usual” number of petals for the species: five is most common, but three, four and six petals are also frequent and there can be many more.

20171205F Max Pixel.jpg

This double tulip is sterile: all its reproductive organs have been turned into petals, a common situation with double flowers. Source: Max Pixel

Double flowers though have a far greater number of petals than normal. Double flowers are rare in the wild, as they tend to be sterile or nearly so, but gardeners like them because they are more colorful than regular flowers and often longer lasting. Usually double flowers show up as mutations, but doubleness can also be an inheritable trait.

Double flowers can originate from different plant parts. Sometimes they come from petals that multiply abnormally and other times, from extra sepals, but in most cases, double flowers result from the stamens that turn into petals, in which case they are called petaloid stamens or just petaloids.

Semi-double flowers have more than the usual number of petals single flowers bear, but less than double flowers. Notably, they usually have non-mutated stamens clearly visible in the center of the flower and are therefore quite fertile.

Flower Heads

An inflorescence is the arrangement of flowers on a plant and includes stems, stalks, bracts and flowers … and the possibilities of how flowers are placed—singly, in umbels, in cymes, in spikes, etc.—are almost limitless. This is a subject for a future Botany 101 blog, but for now, I simply want to clarify the situation of flower heads, because they cause much confusion among gardeners.

A flower head, also called capitulum, is the compound inflorescence seen in the huge Asteraceae family (daisy family), containing more than 22,000 species. It’s confusing, because while it looks like a single flower—apparently a circle of petals surrounding carpels and stamens—it’s actually something quite different.

20171205G ENG pixio.com.jpg

A typical Asteraceae inflorescence. Source: pixio.com and laidbackgardener.blog

Instead the flower head is made up many tiny flowers (sometimes called florets) closely packed together. Some of the best-known examples are sunflowers, dandelions, daisies and thistles. Often, there are two types of florets: tubular florets in the center that form a disc (they’re called disc flowers) and that are generally hermaphroditic and fertile and ray flowers with one large lobe that form a circle around the disc, giving that typical daisy appearance and thus mimicking the petals of simple flowers. Often, but not always, ray flowers are sterile and serve only to attract pollinators to the fertile disc flowers in the center.

Theoretically, you shouldn’t call an Asteraceae “bloom” a flower, but always use the terms flower head, inflorescence or capitulum, but I must confess that I break this rule regularly. Indeed, often voluntarily. It’s too easy to call something that looks like a flower a flower. I do it when I have no specific reason to point out the difference, although I sometimes do slip in the word inflorescence just so any botanists reading the text know I really do know the difference.


And there you go. Hopefully this article helped demystify the complex subject of the flower!20171205B Petr Dlouhý, Wikimedia Commons

Advertisements

Garden Myth: When a Plant Doesn’t Bloom, It’s Because It’s a Male

Standard

20170407B.jpgIt’s always a bit mysterious when a plant doesn’t bloom. After all, most bloom annually. How then to explain why a plant doesn’t flower at all?

Often one of your friends suggests what seems to be a logical answer. “If your plant doesn’t flower, it’s because it’s a male.” Well, that does sound logical… but it’s totally false. You see, male plants also bloom. In fact, they have to. If they didn’t and therefore didn’t produce pollen, how would female flowers receive the pollen they need to produce seeds?

Perfect and Imperfect Flowers

20170407CENIn fact, the vast majority of flowering plants, about 90%, are said to be “perfect”: that is, they are hermaphrodites (bisexual) and carry both stamens (male) and at least one pistil (female) in the same flower.

When a flower does not have both sexes, it’s said to be imperfect. Some plants, for example, are monoecious: there bear separate male and female flowers on the same plant. Squashes (Cucurbita spp.), begonias (Begonia spp.) and most conifers belong to this group.

About 6% of plants are dioecious, that is, they produce male flowers (with stamens) and female flowers (with a pistil) on separate plants. This is notably the case with hollies (Ilex spp.) and kiwis (Actinidia spp.). Do note though that both plants, although one is male and one is female, do bloom.

So Why Do Some Plants Not Bloom?

Let’s return to the initial problem: how to explain why a plant doesn’t flower. Here are some of the (many) possibilities:

20170407A.jpg

It can take years before a tree first blooms.

  • It’s not mature enough. True enough, some plants bloom within months of sowing, but others wait several years before they start. In the case of large trees, it’s not at all unusual for it to take 40 years before the first flowers appear.
  • It may not bloom annually. There are plants that bloom only every two years, and others that flower even less frequently. If you take notice of it in an off year, no, it won’t bloom.
  • It has been incorrectly pruned. This is a common occurrence in home gardens. If you prune a plant while it bears flower buds, even if they’re still nearly microscopic, that will keep it from blooming. To avoid this situation, and if you have a good reason to prune (few plants need to be pruned on a regular basis), always prune it after the plant blooms.
  • Maybe it did bloom, but you didn’t notice. Not only are some flowers pretty insignificant, but they may also bloom for such a short period or at such odd hours that it’s unlikely you’ll notice them.
  • It’s not growing under the right conditions. This is the number one reason a plant doesn’t bloom. The plant may lack light or receive too much light, the soil or air may be too humid or too dry, it may be too cold or not cold enough in the winter or too cool or too hot in the summer, the soil may be too poor (or too rich)… and the list goes on and on. In fact, three cheers for the capacity of plants to adapt to new conditions, because it’s almost surprising that a plant removed from its natural environment and cultivated in a very different climate still manages to bloom, yet so many do.

As a laidback gardener, it’s up to you to grow the plant under conditions the most closely meet its needs. Then all you have to do is wait patiently for it to start to flower!20170407B

A Seed-Starters Glossary

Standard

20150414April is the main season for sowing seeds of vegetables, annuals, herbs, etc. indoors. Garden centers are presently full of displays of seed packets of all kinds and there is an even bigger choice when you order by catalog, either by mail or online. But what about the mysterious vocabulary seen on the back of seed packs and in printed and virtual seed catalogs? For many beginners, it’s like a foreign language! To help you, here are a few terms you may encounter and their definitions.

Acclimatization: A vital action taken just before transplanting seedlings outdoors. It simply means to place the seedlings, still in their pots, outdoors in the shade for 2 or 3 days, then in partial shade for 2 or 3 days, then in full sun for 2 or 3 days. The seedlings are now “hardened off” and ready to transplant to their permanent location.

Annual: a plant that completes its life cycle, from germinating to seed production, in one single year, then dies. Ex.: cosmos, marigold, sunflower.

Biennial: a plant that completes its life cycle in two years, usually producing a rosette of leaves the first year and flowers and seed the second. It dies after seed production. Ex.: foxglove, parsley.

Perennial: a herbaceous plant (not woody) that lives more than two years and that blooms more than once. It does not die after flowering.

Botanical Name: see Scientific Name.

Bush-type: see Non-Running.

Chlorosis: when leaves contain insufficient chlorophyll. They are often pale, yellow, or yellow-white. An iron deficiency, or lack of iron, is a common cause of chlorosis. See Nutrient Deficiency.

Cold Treatment (Stratification, Vernalization): subjecting to cold seeds that must go through a cold period before germinating. Usually they are sown in pots and placed in a refrigerator for several weeks before exposing them to heat. An alternative is to sow them outdoors in the fall in a cold climate where they will naturally undergo cold temperatures. Many perennials, shrubs, and trees from temperate climates require a cold treatment.

20150414BCotyledon: a seed’s first leaf, usually simple and often very different appearance from mature leaves. Most seedlings have two cotyledons, but there are seedlings with only one cotyledon, more than 2 cotyledons and without any cotyledon.

Cross-Pollination: The transfer of pollen from the anther of a flower of one plant to the stigma of a flower of another plant of the same species. It is usually carried out by insects, birds or wind.

Cultivar: a plant raised and multiplied by humans, that does not exist in nature. It’s name is typically written between single quotes (‘   ‘). The name derives from “cultivated variety”. Ex.: in Cosmos bipinnatus ‘Sonata White’, ‘Sonata White’ is the cultivar name.

Determinate: said of a tomato plant (and a few other plants) in which each branch ends in a cluster of flowers, which therefore limits its upward growth. Determined tomatoes make fairly small plants and don’t always need staking. They tend to produce all their tomatoes at about the same time.

Indeterminate: said of a tomato plant (and a few other plants) whose flowers appear in the axils of branches and not at the stem tip. Therefore the stem continues to grow in height throughout the growing season. These tomatoes need staking or a large tomato cage. They may produce less fruit at once than a determinate tomato, but usually do so over a long harvest season and often give double or triple the yield of a determinate tomato.

Dioecious: refers to a plant whose male and female flowers are borne on different plants. The asparagus is dioecious.

21050414D

On this female flower (monoecious), you can see the ovary that will later become the fruit.

Monoecious: refers to a plant that produces separate male flowers and female flowers on the same plant. Often the female flower is easily recognized because it has a small ovary at its base in the shape of the fruit to come. Squash, melons and cucumbers are monoecious.

Perfect Flower (Bisexual Flower, Hermaphroditic Flower): said of a flower that has both male and female organs, thus both a stigma and stamens. This is the most common situation in nature.

Direct Sowing (Direct Seeding): sowing a plant directly outdoors where it is to grow. Beans, marigolds, and corn are often direct sown.

Do not cover: said of a seed that should not be covered with soil at sowing, usually because it is either very fine or requires light to germinate, or both.

GMO: genetically modified organism. Said of a plant into which humans have inserted genetic material from another plant or even an animal without going through pollination. There is, for example, corn containing the genes of Bt genes (a bacteria) and varieties of canola and soybean which with inserted genes that make them resistant to herbicides.

Hardening Off: see Acclimatization.

Heirloom Vegetable (Heirloom Plant): an old variety. Some authorities consider a plant having been introduced more than 50 years ago to be an heirloom variety, others prefer the definition “before the 1940s”. Most heirloom vegetables are produced through open pollination, that is pollination carried out by insects, birds, or wind. Examples.: ‘Brandywine’ tomato, ‘Golden Bantam’ corn, etc.

Hybrid: plant resulting from the crossing of two different breeds, species or genera. F1 hybrids are the most common type of hybrid and are the result of a first generation cross (F1 means “1st filial generation”). Usually, F1 hybrids are more robust than non-hybrid plants, but more expensive, because they have to be manually pollinated in a greenhouse setting. F2 hybrids, less common on the market, are seeds of F1 hybrids, thus the second generation (2nd filial generation). They are cheaper, as they are generally produced by natural pollination, but tend to give less reliable results than F1 hybrids.

Last Frost Date: the date used to calculate when to plant tender plants, referring to the approximate date when you can expect the last spring frost to occur. On seed packs and in seed catalogs, you’re often told to plant or sow outdoors so many weeks (6 weeks, 8 weeks, etc.) before the last frost date. You can ask a local garden club or garden center for the last frost date in your region, then simply count backwards to find the right date for sowing seeds.

Latin Name: see Scientific Name.

20150414E

In the case of a nutrient deficiency, it’s hard to tell which mineral is missing: in this leaf, the damage could be a lack of iron or of nitrogen. Applying a complete fertilizer will solve both.

Nutrient Deficiency: results from the lack of a vital mineral in the soil (phosphorus, potash, nitrogen, zinc, boron, iron, etc.). It can have various symptoms include discolored or deformed leaves or slow growth. Treatment with a complete fertilizer (containing all the trace elements, such as a seaweed or fish fertilizer) will usually overcome a deficiency.

Organic: various definitions. Organic seeds are harvested from plants that have not been treated with synthetic (that is to say, chemical) pesticides or fertilizers. Organic pesticides are derived from natural sources, not from chemical synthesis.

Running: said of a squash with long creeping stems that require a lot of space in the garden, like a pumpkin. This is the natural state for squash.

Non-Running (bush type): said of a squash that produces a short stem and a rosette, taking up less space in the garden than a running squash. The zucchini is the best known non-running squash.

20150414CPeat Pot: pot made of pressed peat, usually used for seedlings that will not tolerate transplanting. The peat pot allows roots to grow right through its sides and bottom and can therefore be transplanted into the garden without removing it. The roots of the plant will then grow right through the peat pot into the surrounding soil.

Pelleted Seed: seeds covered in a product (usually clay) which facilitates their handling.

Pinching: removal of a plant’s terminal bud (bud at the end of the stem). Pinching stimulates branching, giving a more compact and attractive plant, but may delay flowering. It is traditionally done by “pinching” the top growth between the thumb and forefinger, but can also be done using pruning shears or scissors.

Requires Light to Germinate: said of a seed that germinates only in presence of light, be it sunlight or artificial lighting. These seeds should be sown without covering them with soil and the pot should be placed in a brightly lit spot.

Scarification: action of filing, nicking, or cutting a seed before sowing it. It can also involve soaking it for several hours in warm water. The goal of scarification is to penetrate very hard seeds (morning glories, hibiscus, etc.) and thus accelerate their germination.

Scientific Name (Botanical Name, Latin Name): it consists of two words, the first being the genus name (name shared with related plants, much like a human surname) and the second, the specific name, which determines the plant accurately. For example, Solanum tuberosum is the scientific name of the potato and Solanum melongena, of the eggplant. Both share the same genus name, Solanum, because they are closely related, while the specific name serves to make it clear to which type of Solanum the writer or speaker is referring. The scientific name is usually written in italics when possible.

Self-fertile: refers to a plant whose flowers can self-pollinate, that is to say that its own pollen can ensure seed production. Most plants are self-fertile.

Self-sterile: said of a plant which has to be pollinated by another variety in order to produce seeds. Many fruits (blueberries, apples, pears, plums, cherries, etc.) are self-sterile or partially self-sterile. It their case, it is always best to cultivate at least two cultivars of the same species nearby, as cross-pollination is necessary for them to produce abundant fruits.

Stratification: see Cold Treatment.

Thinning: removing some seedlings or fruits in order to allow room for others to grow better. Usually this is done by cutting the excess plants or fruit stalks the base.

Transplanting: moving a plant from one place to another. In the case of seedlings, this is usually from the pot in which they were sown into a larger pot or into the ground.

Treated seed: seed has been treated with a fungicide to prevent rot in cold or wet soils. This treatment is not considered acceptable to organic gardeners.

Untreated Seed: seeds that have not been treated with fungicides and therefore acceptable in organic gardening.

Vernalization: see Cold Treatment. It can also mean subjecting growing plants to cold to stimulate flowering.