Some things we take for granted, but when we take a moment to wonder, we may realise how little we know about them.
I enjoy cooking, so I would say this post was inspired by the first question about bell peppers, as you will see later. In truth, more than half of the questions I only came up with after I started writing — I didn't want to just talk about edible vegetables and fruits, but since I don't have a garden or a lot of house plants, it was harder for me to think of questions related to them. Still, I tried my best to strike a balance between a wide range of topics, so hopefully you’ll find at least one that blows your mind!
Bell peppers of different colours (orange, red, green, yellow).
Q1. Why are there different colours of bell peppers?
A1. The colours indicate different levels of ripeness. For most variants, green and yellow fruits are unripe, and they gradually turn red as they ripen. Some exceptions include Permagreen, which — as the name suggests — stay green even after ripening. There are also white, purple, chocolate and candy cane striped variants of peppers, but they all taste mostly the same: the riper the fruit, the sweeter and less bitter it becomes!
Here’s an additional fact to impress the botanists. Although bell peppers are mainly served as vegetables, they are botanically considered fruits and, more specifically, classified as berries.
Grass on a lawn in front of a house.
Q2. Why is the grass in my backyard so resilient?
A2. Grasses grow from their base, so even after a nice mow of your lawn, they can recover really quickly!
For a deeper explanation, we must consider the identity of grasses as monocots, which are a type of flowering plant whose seeds typically only possess one embryonic leaf (cotyledon). They also differ from the other group, dicots, in the positioning of their meristems — a type of plant tissue in which unspecialised cells divide, much like the stem cells in humans. Monocots like grass contain basal or intercalary meristems, allowing growth from the base, while dicots like olive trees contain apical and lateral meristems, allowing growth from the tip or their sides (e.g. thickening of a tree trunk). This means that the youngest part of a grass blade is located at the bottom, whereas for an olive tree branch, it is found at the tip.
Broccoli crown surrounded by leaves.
Q3. What is the relationship between broccoli and tenderstem broccoli?
A3. Broccoli is cultivated from Brassica oleracea by selectively breeding plants with larger, compact flower heads, eventually giving rise to the broccoli crowns that we eat. Tenderstem broccoli, on the other hand, is a hybrid between two different cultivars of Brassica oleracea: it is the product of breeding broccoli and gai lan (芥蘭; “Chinese kale”) together.
It may be a bit confusing at first — most people are surprised to learn that broccoli, gai lan, brussel sprouts, cabbage, kale and cauliflower are all the same species (Brassica oleracea), just different variants of it [1]. Tenderstem broccoli is simply a combination of two of them, resulting from the innovative efforts of the Sakata Seed Company. They dedicated eight years to developing this hybrid and named it Aspabroc [2]. Meanwhile, the more common name of Broccolini is now a trademark of the Mann Packing Company [3].
Left: Typical, mono-colour tulips. Right: Rembrandt (breaking) tulips.
Q4. What are Rembrandt tulips?
A4. These tulips are named after Rembrandt Harmenszoon van Rijn, a Dutch painter who is known for painting breaking tulips. Unlike normal tulips, breaking tulips are characterised by streaks in their petals, which appear to “break” the typically single colour of the flower. They originally arose after an infection by the tulip breaking virus (TBV), or any one of the five plant viruses from the family Potyviridae. Their unique appearance actually made them pretty popular and was favoured over the traditional tulips in the seventeenth-century Netherlands! However, the virus is ultimately harmful to the plant, and breaking tulips are often more fragile, has shorter stems and are smaller than their healthy counterparts. Through breeding, rather than viral infection, “modern” variants of breaking tulips are created, giving rise to the Rembrandt tulips we know today.
Chopped okra, with the cross section and seeds visible.
Q5. Why is okra so slimy?
A5. The part of okra (Abelmoschus esculentus) we eat, the green seed pods, contain mucilage, which turn into the characteristic “slime” when cooked. Mucilage is a gluey substance composed of cell wall polysaccharides and is produced by almost all plants, as well as some microorganisms. The polysaccharides serve unique functions across different plants: trapping insects in carnivorous sundews (Drosera) and butterworts (Pinguicula), concentrating pathogen-resistant compounds on the surface of basil seeds to protect them, adhering elephant apple (Dillenia indica) seeds to the fruit to aid in dispersal, and many more [4].
Left: Plant with typical, purple and oblong aubergines. Middle: Plant with striped aubergine. Right: White aubergine near the ground.
Q6. How did eggplants (aubergines) get their name?
A6. While the eggplants most people see in the supermarket are purple and ovoid, the variant from which the name was derived is white and round, much like an egg [5]. Because of this, they are also called garden eggs! The name aubergine, however, has a more complicated background. It came from the Arabic word bāḏinjān (listen), literally meaning “the eggplant” [6]. This is because bāḏinjān in itself is a loan-word — a word borrowed from another language — with possible origins in a family of languages called the Dravidian languages.
However you decide to call the fruit (yes, it’s another “vegetable” that is botanically a berry), there are again many other cultivars — mostly grown in India and Asia — that may surprise you, from green ones (”Thai green”) to bicoloured ones with gradients (”Rosa Bianca”) and stripes (”Udumalapet”)!
Left: Bamboo forest. Right: A cut bamboo culm (stem) showing the hollow internode.
Q7. Why is bamboo hollow?
A7. Simply put, bamboo is a grass, and the stems of most grasses are hollow. Most of the bamboo we see is the plant’s stem — scientifically called culm — and the rings along the stem are the nodes, or “knuckles”, which are the only solid parts of the tube. Now, you may be imagining a blade of grass and thinking it’s more flat than cylindrical or tubular, and you wouldn’t be wrong. The grass we see in gardens and sidewalks just have more prominent leaves, but their narrower and shorter culms are still, indeed, hollow.
To answer why these hollow stems came to be, however, is a much harder task. We’d have to figure out the driving force behind the evolution of these culms, and there’s hardly a good answer out there. A study in 1959 compared the internodes (sections between nodes) of 133 species of grasses and found a correlation between the occurrence of solid internodes and hotter, drier and windier climates [7]. In other words, grass species with solid culms tend to live in arid regions, while those with hollow culms tend to live in temperate, artic or alpine habitats. This could suggest selective advantages of hollow and solid stems in increasing stress tolerance in different conditions, but no causal relationship has been established. Either way, we can still marvel at how bamboo, despite its hollow culm, is as strong as one of the most important structural materials in the world!
Left: Peanuts with shell (pod) intact. Middle: Hazelnuts with shell intact. Right: Almonds on a plant, with the fleshy outer layer split open and showing the hard almond inner shell inside.
Q8. If peanut is not a nut, then what is a true nut?
A8. Most of you might already know that peanuts (Arachis hypogaea) are legumes from the family Fabaceae, which contain flowering plants that form symbiotic relationships with nitorgen-fixing bacteria and are ecologically important in mediating soil nitrogen levels. In that case, what really counts as a nut? Botanically speaking, nuts are fruits (at this point, everything is a fruit!) that have a hard nutshell, derived from the hardening of the ovary and protecting a usually edible kernel. True nuts are also indehiscent, which means the shell does not open naturally to release the seed. Peanuts, on the other hand, have a soft, papery shell that is actually the pod of the legume, much like pea pods.
Hazelnuts (Corylus), chestnuts (Castanea) and acorns (Quercus and Lithocarpus) are true nuts, but almonds (Prunus amygdalus), pecans (Carya illinoensis) and macadamia (Macadamia integrifolia) are not. They are drupes, which are also indehiscent fruits, but the seed is attached to a hard inner shell (endocarp) called the “stone” or “pit” — in contrast, true nuts are loose and free inside their nutshell. The pit itself is surrounded by a fleshy part. If this sounds familiar, that’s because peaches, cherries and plumps are also drupes! There are a lot more “culinary nuts” that are not true nuts, but I could go on forever. So, what’s your favourite nut?
Q9. Why do plants droop at night?
A9. If you are very observant, you might notice that some plants and vegetation look different at night than they do during the day. There are many possible explanations to this phenomena, and one of them is foliar nyctinasty (FN), which describes the change in leaf orientation in some plants that seems to follow a circadian rhythm. During the day, the leaves are spread out and in a horizontal orientation that maximises surface area for photosynthesis. During the night, however, the leaf blades acquire a vertical position. Since Darwin’s times, many hypotheses have been proposed to explain this behaviour. One of the stronger ones state that FN is used to indirectly defend plants from herbivores by 1) assisting killing of herbivores by nocturnal predators and 2) discouraging foraging behaviour of herbivores [8].
FN reduces the surface area covered by vegetation by making the plants more columnar and thin in shape. This creates holes or interstices between the plants, reducing “physical clutter” in the landscape. While smaller prey can still hide behind the nyctinastic plants, larger preys will become more visible to nocturnal predators, especially ones in the sky.
That’s not all – there are other ways FN can assist predation. Vegetation is known to absorb sounds, so without the vast and dense layer of foliage to disperse the noise made by preys, predators like bats can detect their targets more easily. Yet another effect of these plants’ nocturnal profile is allowing odour from preys to reach the predator more directly. This is relevant for parasitoid wasps, which rely on odour released by animals to hunt.
Finally, because FN reduces foliage cover, herbivores become more vulnerable to predators and are discouraged from foraging at night.
Who knew a simple change in leaf orientation can help plants escape predation in so many ways?
Left: Lavenders in a field. Middle: Rosemary plants. Right: Lemons on a tree.
Q10. Which plants are best at repelling mosquitoes?
A10. In most insect repellents, the active ingredient is a chemical compound called diethyltoluamide (DEET). It turns out that a lot of plant extracts, specifically the essential oils of lavender (Lavandula officinalis) and eucalyptus (Eucalyptus globulus), are almost just as efficient as DEET in repelling Anopheles stephensi, a species of mosquito that is the primary vector of malaria [9]. Other plants, such as lemon, basil and rosemary, also have relative efficacies greater than 90%, making them suitable and safer alternatives of DEET. Although plant extracts are definitely more potent and efficient, it wouldn’t hurt to keep a pot of these plants or herbs around the house!
Answering these questions sent me on a whole journey into some rather interesting corners of plant diversity, applications and botanical terms. I have no doubt I will be back with another ten questions some time soon! In the mean time, stay safe, and stay curious!
References:
Mabry ME, et al. The evolutionary history of wild, domesticated, and feral Brassica oleracea (Brassicaceae). Mol Biol Evol. 2021, Jun, 22;38(10):4419–4434.
Sakatahomegrown.com. Broccolini ideas [Internet]. 2017. Available from: https://sakatahomegrown.com/homegrown-articles/sakata-home-grown-presents-broccolini-ideas/.
Trademark status and document retrieval (TSDR). Broccolini (Reg No. 2365625) [Internet]. 2000. Available from: https://tsdr.uspto.gov/#caseNumber=75446875&caseSearchType=US_APPLICATION&caseType=DEFAULT&searchType=statusSearch
Tsai A, McGee R, Dean GH, Haughn GW, Sawa S. Seed mucilage: Biological functions and potential applications in biotechnology. Plant Cell Physiol. 2021, Jul, 31;62(12):1847–1857.
Etymonline.com. Eggplant [Internet]. Douglas Harper. Available from: https://www.etymonline.com/word/eggplant#etymonline_v_32168.
Etymonline.com. Aubergine [Internet]. Douglas Harper. Available from: https://www.etymonline.com/word/aubergine#etymonline_v_18922.
Brown WV, Harris WF, Graham JD. Grass morphology and systematics. I. The Internode. Southwest Nat. 1959, Oct, 24;4(3):115-125.
Minorsky PV. The functions of foliar nyctinasty: a review and hypothesis. Biol Rev Camb Philos Soc. 2018, Jul, 11;94(1):216–29.
Shooshtari MB, Kashani HH, Heidari S, Ghalandari R. Comparative mosquito repellent efficacy of alcoholic extracts and essential oils of different plants against Anopheles stephensi. Afr j pharm pharmacol. 2013, Feb, 15;7(6):310-314.