By their fruits, ye shall know them… The following pages describe different kinds of fruit from perspectives of the Cook, the Systematist, and the Morphologist. –
A Farmer’s Market from three Perspectives…
Some food plants we encounter on a daily basis produce such characteristic fruit that it is useful to have a word specific to each distinct structural type. Using technical terms forces us to think more carefully about how the fruit of two kinds of plants may be similar, or why they are considered different.
The necessary comparisons bring us to critical analysis of form, a study called Comparative Morphology. A Morphologist (in this case, a Carpologist) would be interested as to how fruit are constructed, and would then define categories to explain how fruit might be similar or different based on growth and development. A person with this mindset would wonder about the kind of fruit we call a Drupe, grouping those types together so as to compare the similarities and differences between a Peach and a Date – two very different fruit we consider to be drupes. In the Carpologist’s marketplace, all drupes would be displayed together, to intellectually savor the similarities and differences.
But there are other ways to look at plants. If a Systematic Botanist organized the produce market based on evolutionary relatedness, the arrangement would be different. Apples, Peaches, Plums, Blackberries, and Strawberries would be in a single display because they are related plants in the Rose family (the Rosaceae), Dates would be with Coconuts, both in the Palm family (the Arecaceae). The melons (Cucurbitaceae) – Cucumbers, Pumpkins, Cantaloupe, Squashes, and Chayote – are large and plentiful, so they’d have their own aisle seasonally.
Finally, a Cook might wish fruit were grouped based on more practical categories, such as texture, flavor, sweetness, seasonality, utility, or shelf-life – components related to how they are employed in the kitchen. The culinary practitioner visiting a produce market would expect to find Peppers and Greenbeans near the vegetables (even though to a Carpologist, these should be with the fruit).
I decided it could be enlightening to examine fruit in a produce market and compare it from the viewpoint of those different thought platforms. So I am sharing the agony of that exploration with you. When I speak of the Cook, I’m thinking about a person who is both experienced and experimental with food preparation. When the text refers to a Carpologist (or Morphologist), it usually refers to Dr. Spjut’s 1994 publication (described at the end of this page). In discussing how a Systematist would deal with a given plant, I call Judd, et al., to your attention, referencing the book Plant Systematics – A Phylogenetic Approach, 4th Edition.
Botanist, Systematist, Morphologist, Carpologist – People who study plants are Botanists. A Botanist who studies how to group or classify plants based on how they evolved and are related is a Systematist (someone who wants to create a system for organizing plants). The Morphologist is a Botanist who studies and compares plant structure, anatomy, and form in order to understand more about how plants grow and develop. As said just a few paragraphs earlier, the Carpologist is a Morphologist whose interests relate directly to the way fruit and cones develop.
WARNING: Extreme Terminology Ahead – Remaining Paragraphs….
A few useful words make the following discussion easier:
Dehiscent and Indehiscent – this means the fruit splits open at maturity (it dehisces), or it does not split open (which means it’s indehiscent).
Carpel – A carpel is the individual segment that is a “fertile leaf” in a pistil. Some pistils have only one carpel (a Bean), while others are made of several carpels (an Orange).
Superior and Inferior – These words tell you whether the pistil in a flower is atop the point of origin for the other floral parts (sepals, petals, stamens), or is buried deeper, seamlessly enveloped in tissue that makes it appear the ovary has a lower, “inferior” position relative to the other flower parts.
Dispersal Unit – Plants show adaptations that increase the chance for being dispersed somewhere distant from the parent plant. That could be a fruit that is eaten by an animal, or a winged seed, or even a twig with fruit and seed attached. What’s clear is the unit or structure that improves dispersal is not always a “fruit.” This term is introduced so as to distinguish between what is dispersed and what is clearly the mature pistil.
I tell students that plant identification is Biblical: “by their fruits, ye shall know them.” This is because people find that fruiting structures are incredibly useful in plant identification and classification, often characterizing genera, or entire plant families. The fruit called a Legume, for example, confirms a plant is in the Bean family. The stem-covered inferior fruit of Cacti is a consistent character for this group, just as the winged samara marks Maples, and acorns correlate to Oaks.
It just isn’t normally that simple, unfortunately. Though fruit types are characteristic of individual plant groups, the curious issue is that botanists fail to agree on a precise definition of the word “fruit”. In general the Reader limits “fruit” to structures produced by flowers of Angiosperms (the flowering plants.) There are many reasons to accept that limitation, most importantly because there is real value in distinguishing between sexually reproductive flowers of Angiosperms and the sexual cones and other structures of Gymnosperms.
But people who study and categorize different kinds of fruiting structures (Carpologists, i.e. carp = fruit) are sometimes more inclusive, pretty much embracing any tissue that encloses, amplifies or promotes dispersal of seed. In the terminologies of carpologist Richard Spjut (A Systematic Treatment of Fruit Types, 1994), Angiosperm (flowering plant) fruiting structures are Eucarpia (true fruit), while Gymnosperms generate Spermatocarpia (seed and associated tissues that function as fruiting structures). That makes for some complex considerations.
To wander into the super-arcane, this broader construct informs Spjut’s very technical definition of Fruit:
“A fruit is a propagative unit developing from one or more fertilized egg cells (or rarely by parthenocarpy) enclosed by integuments and attached to megasporophylls, or a megaporophyll-scale complex, in a strobilus, cone, gynoecium, concrescent gynoecia, or gynoecia that disseminate together at the time it or its seed(s) are dispersed from the plant, or just prior to germination on the plant, and it may also include any other attached scales, bracts, modified branches, perianth, or inflorescence parts.”
For pure complexity and bravado, Dr. Spjut’s definition is spectacular. But for teaching, it makes other concepts more difficult to convey, so I limit fruit to the flowering plants. That allows me to say more simply that a fruit is a mature ovary and associated dispersal tissues.
I’m not the only one who thinks this way. Dr. Spjut’s technical definition is not universally adopted. In reading plant literature, different authors accept varying approaches:
- By all accounts, fruit includes the mature pistil of a flowering plant, along with directly associated floral tissues. (ex: Orange, Banana.) Fruit from inferior ovaries (Guava, Banana) include other layers of floral tissues (sepal, petal, stamen).
- Fruit can include vegetative tissue that encases the mature pistil, such as stem tissue (ex: Apple)
- Fruit often describes a somewhat cohesive structure that includes multiple mature but separate pistils that were formed in a single flower (ex: Raspberry, Magnolia)
- Fruit sometimes describes an apparently single structure that is actually made of mature pistils from many flowers (ex: Mulberry, Pineapple)
- In some texts, the word fruit can describe structures that are both aggregate and accessory (add to), such as flower, leaf, and/or stem tissue. (ex: Strawberry, Pineapple). When the structure includes many flowers, it is equivalent to an “infructescence.”
- Fruit might, unfortunately, refer to fleshy dispersal units that do not even include reproductive parts. This is beyond the pale for me. (ex: the fleshy Marañon, which is the peduncle (stem) that supported the flower and mature pistil of cashew)
- As was pointed out earlier, Fruit could indeed refer to seed-bearing structures of Gymnosperms, such as Taxus. The Reader does not refer to those as fruiting structures because no carpels (therefore no ovaries or pistils) are produced.
If you are confused, you are not alone. And things only get more confounding. Botanists also disagree on words that rightly describe different kinds of fruit. The lesson here is that each group of plants has evolved specializations not precisely parallel or equivalent from one clade (evolutionary branch of the plant kingdom) to another. Even when the fruiting structures produced by two different plant groups appear similar, they are likely very different. So for more precision, specific terms proliferate
This makes for a minefield of jargon that may seem ridiculous. Regardless, terminologies that allow us to communicate structural similarities and differences are useful. We simply must remember that the great variation (both internal anatomy and external morphology) from one group of plants to another means there are times when different categories and terms used for fruit are highly artificial.
By “artificial” I mean there are terms that provide convenient ways to group somewhat comparable structures, even when those structures do not have exactly the same origins and were not constructed in the same way. For example, both Peach and Date are called Drupes, because the fruit wall has a soft outer layer and a hardened inner layer (a stone) which encloses the single seed. In Dr. Spjut’s lexicon, it isn’t important whether the two fruits grew in exactly the same way, or that the hard and soft tissues have the same anatomies. We are communicating simply the fact that in each of these examples the “stone” we think of as a “seed” is really made of a hard, inner layer of the fruit wall, inside which you will discover a single seed.
Lest you think that is moronic (like who cares?), remember from other definitions in the Reader that a pistil forms from one or more carpels (fertile leaves), inside which seed are produced. Therefore, deciphering the structure of each carpel tells us how the pistil is constructed, so it’s worth taking a few moments to worry about these terms.
OK – the simplest arrangement for seed-producing in a flower is one folded “leaf”, which we call a carpel. The swollen base of that carpel is the ovary, where ovules (future seed) are produced. At its tip, the carpel tapers to a narrow stipe (called the style), producing a landing place for pollen – the stigma. This simple 1-carpel arrangement is what we see in beans; it is the flower’s pistil.
Different kinds of plants are known for other arrangements. A flower can produce more than one carpel, each developing individually. We see this condition in Magnolias, Roses, Sedums, and many common plants. Because each free carpel is also a pistil, then the flowers of those plants produce many pistils.
Things become more complicated (or simpler, according to your viewpoint) when carpels in a flower fuse to make a single structure. Think of an Orange. In the Orange we see several segments, each of which is a carpel. But they are fused into a single structure (we say they are “connate”). Now we have a flower with many carpels, but only ONE pistil….
Understanding the development of a maturing pistil is part of appreciating how plants build themselves, and is crucial to making sense out of the forms you see. Otherwise, when do you know you have your hands on a seed? Remember each seed began as a tiny ovule formed in a carpel. Botanists keep track of what happens to the ovule as it matures into a seed.
It’s multi-layered and genetically fascinating. The outer tissue (integument) becomes the the seed coat (testa), and is genetically like the parent plant. Inside, a mature seed might have residual parent material (nucellus/perisperm), but in most examples you find the bulk of the seed sports new genetic combinations (the embryo & in some plants, the triploid endosperm).
So producing a mature seed is a complex ordeal, and following the development informs our understanding of the genetic makeup. There are so many stages that it almost seems impossible this happens so regularly and seamlessly. When you read a botany text, the author little other choice than to lay out the entire course of events, provide terminologies that specify process and products along the way, and hope it all makes sense. This means that each word carries incredible freight, and a lot of words are needed. Just in case you wish to pursue the topic of embryology further, here, in sequence, are some of the most common terms you will encounter:
- Flower: Peduncle, Sepal, Calyx, Petal, Corolla, Perianth, Tepal, Stamen, Androecium, Pistil, Gynoecium, Zygomorphic, Actinomorphic, Pollination Strategy, Nectar, Nectary, Extra-Floral, Reward, Co-evolution, Anemophily.
- Female line: Carpel, Ovary, Pistil, Style, Stigma, Ovule, Funiculus, Integument, Nucellus, Megaspore Mother Cell, Meiosis, Megasporagenesis, Haploidy, Megaspore, Megagametophyte, Egg Sac, Mitosis, Polar bodies, Synergids, Antipodals, Gamete/Egg, Chalazal end, Micropyle, Fusion, Endosperm.
- Male line: Micropore Mother Cell, Meiosis, Microsporogenesis, Haploidy, Microspore, Microgametophyte, Pollen Grain, Mitosis, Pollination, Pollen Tube, Gamete, Sperm Nucleus, Tube Nucleus, Vegetative Nucleus, Fusion, Triploidy.
- Fertilized Egg: Fertilization, Zygote, Diploidy, Endosperm, Triploidy, Radical, Root Apical Meristem, Shoot Apical Meristem, Epicotyl, Cotyledon, Hypocotyl, Plumule, Testa (Seed Coat), Hilum, Dormancy.
- Fruit (Mature Pistil): Carpel, Placenta, Connate, Adnation, Ovary, Style, Stigma, Post-pollination Phenomena,
We are not going there, at least not deeply. The warren of terms is presented only to reinforce the concept that each term has a specific meaning implying origin, developmental morphologies, anatomies, genetics, function, and future.
In the end, we come to fruiting structures and dispersal units, which gives birth to an entirely new set of terminologies – all invented to help us describe, categorize, and explain the many different kinds of fruit. Wading about in that terminology is where we are headed.
The discussion begins by describing the kinds of fruit people consume – a Farmer’s Market glossary of fruit types.