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What are Stipules and Bracts? · Hydroponics Daily

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  Hi, welcome back to Hydroponics Daily. Today I thought I would do an episode
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  on plant anatomy and today's subject is stipules and bracts which are often
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  confused with flower parts.
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  So the reason for this is that bracts are actually leaves.
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  They're specialised leaves though associated with flowers. So they might be
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  green or they might be colourful.
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  So a great example
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  is bourgenvillia the purple flower the purple
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  vine that you see in mediterranean climates i've
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  got one in my greenhouse and it produces tiny white flowers that are surrounded
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  by big purple leaves that might be confused for flower petals however they're
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  not petals because they contain the same structures that a leaf would so they've
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  got a peteol which is a leaf stalk they've got a.
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  And, crucially, they'll have stomata in their epidermis for gas exchange.
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  And they'll probably do some photosynthesis as well, which you really couldn't rely on.
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  A bract, sorry, a petal for. Other examples of plants where the most showy part
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  of the plant is a bract is dogwood.
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  That's another one. And lots of euphorbias.
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  In fact, most euphorbias, including ponsetia,
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  which is very important economically for
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  ornamental horticulture especially in the winter and in
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  at christmas so poinsettias are what you buy
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  at christmas and also now increasingly the yellow the
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  orange ones during halloween so there
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  you are buying them for their showy bracts and that's important because the
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  reason it's important that they're bracts and economically important is that
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  because they've got this leaf stalk they've got a the end of the leaf stalk
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  is something called the abscission zone and if you stress.
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  Euphobias and poinsettias they will
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  they will release ethylene at this abscission
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  point and the leaf will just fall off that's what abscission is
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  just the leaves falling off it won't senesce and so if
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  you flood a poinsettia that all the all the colorful showy
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  red leaves or pink leaves or orange leaves will fall off if
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  you take them outside in your car from the supermarket to
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  the to your car and it's too cold they'll get stressed
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  and the bracts will fall off if you drop them
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  on the floor they'll the bracts will fall off i once
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  went to a talk by a german poinsettia breeder and
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  it was hilarious because all the tests were named
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  like typical german names so like the
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  um the the they would test whether the plant was
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  robust enough to withstand dropping and the test was called the drop and plant
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  plant and test and it was like really logical names the drop and plant and they
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  would score the plants from one to ten on how resilient they were for their bracts falling off.
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  So other plants where bracts are important are bananas and cannabis and hops.
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  In hops, the bracts are the tiny little leaves that surround the female ovaries
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  and the glands that produce the wonderful scents and terpenes of a hop.
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  Hops just smell absolutely delicious is to me and
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  the bracts are what keep it
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  healthy and and stop pests and disease from getting in and things like this
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  and hopefully you know keep it looking good the bracts are also the first things
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  to turn brown when the weather's bad so you know we've had talks with our hop
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  growers and they've said that when they apply our seaweed extracts and humic
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  acids and fertilizers and.
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  The bracts stayed green and they were able to take them to the show and win
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  awards, whereas their competitors, all their bracts had turned brown.
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  So the leaves wouldn't have turned brown, the ovaries inside wouldn't have turned brown.
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  And again, in other plants, the bracts are very important.
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  So in other plants like cannabis, the bracts contain lots of the trichomes.
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  It's not just the reproductive organs.
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  And the same for what we're going to move on to,
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  and that is the stipules so stipules are not
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  leaves they are growths though normally green
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  in color but they can vary and they're at
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  the base of the leaf stalk the base of the petiole and
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  so they're like they might be like a look like a
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  tiny little leaf or a scale and the
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  most look often or you know so stipules are
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  are strange and they have a number of different uses in plants
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  and they might not be obvious to you what that use is
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  so it depends on the plant so like in
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  a euphorbia which look a lot of euphorbias look like cacti so we said about
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  poncetti as a type of euphorbia but in africa there are a lot of euphorbias
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  that look like cacti and there the spine is a stipule other stipules like in
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  roses they just look like a little bit of leaf on the end in the oil crop.
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  Jatropha which is very common in india and other
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  tropical places where it's very dry the stipules
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  are actually like glandular hairs so not trichomes because
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  they're much bigger than this and then in a
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  lot of tree species broadleaf tree species the
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  stipule acts as almost like a covering to
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  protect the developing young leaf so some
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  stipules may be present when the leaf is developing and
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  then fall off other leaves when it's growing out and then a
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  lot of stipules just stay on for the whole of the time that the plant is alive
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  so for like some stipules like those in say cannabis it's thought that they
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  have a protective mechanism because they've got trichones on them so they are
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  protecting the young developing flower bud from attack by pests,
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  and then you know there's like the the euphorbia they're
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  a spike so they're obviously protecting it from attack by insects
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  and but more commonly animal mammals and birds
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  and things like that they might want to eat it and then as i
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  said the glandular ones might be feeding beneficial organisms however the function
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  might not be known and so you might find like a rose stipule who knows what
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  root function that has it might be just a bit of additional photosynthesis it
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  might be obviously as we said protecting the young leaf from as it developed
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  and then photosynthesis later on.
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  It's difficult to say and there isn't an
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  obvious reason for the stipule you might say
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  that it's vestigial just like the appendix in
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  the human body is was thought to be vestigial because
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  no one could understand a reason for humans having
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  it and so if botanists said
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  that there was no use for it say it's vestigial it's an evolutionary hangover but
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  now we know that the appendix in the human body is
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  a really good source of beneficial bacteria it
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  stores the beneficial bacteria in our guts when we have an
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  episode like imagine you drank a load of whiskey and
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  you killed off all the bugs in your stomach and then you had a
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  load of antibiotics and killed off all the bugs in your stomach you need those
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  beneficial bacteria back and then because the appendix was out well out of the
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  way of all that whiskey and antibiotics you can repopulate with the the microbes
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  so people didn't understand the benefits of the microbiome until very, very recently.
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  We still don't know all the benefits.
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  And so just because we don't know a reason for, say, plants having stipules
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  in certain species doesn't mean they don't have an evolutionary advantage.
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  So the word vestigial is a bit old hat nowadays.
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  I think in peas and beans, the stipule is
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  like the tendril as well that helps them climb up the
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  vines so obviously that's a
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  very important function that that stipule
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  is undertaking so that's been hydroponics daily for
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  today the importance of bracts and
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  stipules certainly in many crops they're very important
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  any resinous crops they're going to be having lots
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  of trichomes on them tendrils for climbing plants the
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  bracts will the stipules will be protecting plants the
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  newly developed leaves from attack and from damage and
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  the bracts of many plants are actually what we grow grow them for the ornamental
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  value so certainly my borgunvillias and my poinsettias at christmas so thank
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  you very much for listening to hydroponics daily for today if it's your first
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  Thank you very much. Goodbye.