# 1) If it's a plant, it \*must\* have green stuff? 2) chlorophyll system with biggest bang for buck? **URL:** \ **Category:** Factual Questions\ **Created:** [May 11, 2015, 1:20am UTC](https://boards.straightdope.com/t/1-if-its-a-plant-it-must-have-green-stuff-2-chlorophyll-system-with-biggest-bang-for-buck/719735 "2015-05-11T01:20:54Z")\ **Posts on this page:** 16\ **Page:** 2
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 13, 2015, 8:42pm UTC](https://boards.straightdope.com/t/1-if-its-a-plant-it-must-have-green-stuff-2-chlorophyll-system-with-biggest-bang-for-buck/719735/21 "2015-05-13T20:42:11Z")
Or, of course, alien plants might use some other pigment that’s _more_ efficient than chlorophyll, whose existence we have no idea of. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [May 13, 2015, 10:51pm UTC](https://boards.straightdope.com/t/1-if-its-a-plant-it-must-have-green-stuff-2-chlorophyll-system-with-biggest-bang-for-buck/719735/22 "2015-05-13T22:51:51Z")
> [@Leo\_Bloom](#): > > Thanks to all. The first part of OP I’ll have to take up with Linnaeus, or whoever it was, besides God, who decided what makes a plant. Traditionally, biologists tried to divide life forms into two large categories, plants and animals. Broadly, plants made their own food and were not mobile, while animals had to eat other organisms and moved about. Organisms like fungi that were not mobile but which couldn’t make their own food were shoehorned into plants. (We now know that fungi are more closely related to animals than plants.) It was even harder to figure out where some unicellular organisms belonged. Green algae were assigned to plants, protozoa to animals, and bacteria were considered fungi and thus also plants. But there were still a lot of problematic organisms. Today, biologists would consider plants to only include the Plantae, those multicellular organisms descended from green algae. Animals are the Animalae, which only includes multicellular organisms. Fungi are their own group. Unicellular organisms, and some multicellalar ones including green, brown, and red algae, are not considered to be plants or animals but are classified in other groups. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 13, 2015, 11:55pm UTC](https://boards.straightdope.com/t/1-if-its-a-plant-it-must-have-green-stuff-2-chlorophyll-system-with-biggest-bang-for-buck/719735/23 "2015-05-13T23:55:07Z")
> [@](#): > > Quoth **Colibri** : > > Today, biologists would consider plants to only include the Plantae, those multicellular organisms descended from green algae. > … > > Unicellular organisms, and some multicellalar ones including green, brown, and red algae, are not considered to be plants or animals but are classified in other groups. I’m not following, here… Are green algae plants, or are they not? ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [May 14, 2015, 4:22pm UTC](https://boards.straightdope.com/t/1-if-its-a-plant-it-must-have-green-stuff-2-chlorophyll-system-with-biggest-bang-for-buck/719735/24 "2015-05-14T16:22:50Z")
There are mutated cacti that lack chlorophyll and can be white (actually slightly yellow), red or orange. (The latter ones still contain chlorophyll relatives.) Originally found when seeds sprouted and didn’t come up green, but commonly propagated by grafting. They require a “host” green cacti to live on for nutrients and they can’t produce enough on their own. Even then they usually don’t live long. (The seedlings really don’t live long unless grafted onto a host.) It would seem to me that if there was a type of plant that could make do with the red/orange stuff instead of chlorophyll, it would be cacti. Slow growing, lots of sun, etc. So I think you pretty much have to be green\*, a parasite, a decay feeder, etc., to have much chance of success. - A lot of non-green plants have chlorophyll + another dye that masks the green a bit. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [May 14, 2015, 4:56pm UTC](https://boards.straightdope.com/t/1-if-its-a-plant-it-must-have-green-stuff-2-chlorophyll-system-with-biggest-bang-for-buck/719735/25 "2015-05-14T16:56:28Z")
> [@Chronos](#): > > I’m not following, here… Are green algae plants, or are they not? There are various definitions and concepts of the [Plantae](http://en.wikipedia.org/wiki/Plant). The most restrictive definition includes only the multicellular land plants, and excludes green algae. A less restrictive definition (Viridiplantae) includes green algae (including unicellular forms) but excludes multicellular brown and red algae. The latter definition defines plants as: > [@](#): > > a group of organisms that possess chlorophyll a and b, have plastids that are bound by only two membranes, are capable of storing starch, and have cellulose in their cell walls ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [May 14, 2015, 6:22pm UTC](https://boards.straightdope.com/t/1-if-its-a-plant-it-must-have-green-stuff-2-chlorophyll-system-with-biggest-bang-for-buck/719735/26 "2015-05-14T18:22:29Z")
> [@Chronos](#): > > Or, of course, alien plants might use some other pigment that’s _more_ efficient than chlorophyll, whose existence we have no idea of. Alien organisms might not even divide easily into the same caregories we have here. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 14, 2015, 6:54pm UTC](https://boards.straightdope.com/t/1-if-its-a-plant-it-must-have-green-stuff-2-chlorophyll-system-with-biggest-bang-for-buck/719735/27 "2015-05-14T18:54:56Z")
True, I should have said “alien photosynthetic autotrophs”. Though even then, not all alien ecologies will even include that (life originated with chemosynthetes, after all). ---
**Author:** ![The\_Other\_Waldo\_Pepper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/the_other_waldo_pepper/32/12370_2.png) [@The\_Other\_Waldo\_Pepper](https://boards.straightdope.com/u/The_Other_Waldo_Pepper)\ **Post date:** [May 14, 2015, 11:04pm UTC](https://boards.straightdope.com/t/1-if-its-a-plant-it-must-have-green-stuff-2-chlorophyll-system-with-biggest-bang-for-buck/719735/28 "2015-05-14T23:04:00Z")
> [@Chronos](#): > > True, I should have said “alien photosynthetic autotrophs”. Like an alien version of euglena? ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [May 15, 2015, 4:44pm UTC](https://boards.straightdope.com/t/1-if-its-a-plant-it-must-have-green-stuff-2-chlorophyll-system-with-biggest-bang-for-buck/719735/29 "2015-05-15T16:44:19Z")
> [@Chronos](#): > > True, I should have said “alien photosynthetic autotrophs”. Would these would be the autotrophs that have begun to drool? ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [May 15, 2015, 8:17pm UTC](https://boards.straightdope.com/t/1-if-its-a-plant-it-must-have-green-stuff-2-chlorophyll-system-with-biggest-bang-for-buck/719735/30 "2015-05-15T20:17:07Z")
What other energy sources might we find alien life hypothetically exploiting? Electromagnetic radiation outside the visible spectrum seems like an obvious one - and chemosynthesis we already know about. What else is there? Mechanical energy from wind or the motion of other fluids? ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [May 15, 2015, 8:52pm UTC](https://boards.straightdope.com/t/1-if-its-a-plant-it-must-have-green-stuff-2-chlorophyll-system-with-biggest-bang-for-buck/719735/31 "2015-05-15T20:52:37Z")
How about thermosynthesis? > **[Thermosynthesis](https://en.wikipedia.org/wiki/Thermosynthesis)** > > Thermosynthesis is a theoretical mechanism proposed by Anthonie Muller for biological use of the free energy in a temperature gradient to drive energetically uphill anabolic reactions. It makes use of this thermal gradient, or the dissipative structure of convection in this gradient, to drive a microscopic heat engine that performs condensation reactions. Thus negative entropy is generated. The components of the biological thermosynthesis machinery concern progenitors of today's ATP synthas Therm... If nanotech robots are the dominant ‘lifeform’ in the universe then mechanosynthesis, possibly driven by electricity, might be more common than photosynthesis. ---
**Author:** ![Measure\_for\_Measure](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/measure_for_measure/32/557_2.png) [@Measure\_for\_Measure](https://boards.straightdope.com/u/Measure_for_Measure)\ **Post date:** [May 15, 2015, 11:24pm UTC](https://boards.straightdope.com/t/1-if-its-a-plant-it-must-have-green-stuff-2-chlorophyll-system-with-biggest-bang-for-buck/719735/32 "2015-05-15T23:24:57Z")
There are a number of trees with leaves that are red year round. Some plants are parasitic. But red leafed trees can have green chlorophyll, masked by other pigments. > **[How Does a Plant With Red Leaves Support Itself Without Green Chlorophyll?...](https://www.nytimes.com/2013/07/23/science/how-does-a-plant-with-red-leaves-support-itself-without-green-chlorophyll.html)** > > A plant with red leaves can still have plenty of chlorophyll, it may just be masked by another pigment. > **[Photosynthesis in Leaves That Aren't Green -](https://baynature.org/article/photosynthesis-in-leaves-that-arent-green/)** > > Q: How does photosynthesis occur in plants that are not obviously green, such as ornamental plum trees with deep purple-colored leaves? \[Paul, Santa Cruz\] A: Photosynthesis (which literally means “light put together”) is that very elegant chemical... ---
**Author:** ![Nava](https://avatars.discourse-cdn.com/v4/letter/n/da6949/32.png) [@Nava](https://boards.straightdope.com/u/Nava)\ **Post date:** [May 16, 2015, 3:58am UTC](https://boards.straightdope.com/t/1-if-its-a-plant-it-must-have-green-stuff-2-chlorophyll-system-with-biggest-bang-for-buck/719735/33 "2015-05-16T03:58:30Z")
> [@purplehorseshoe](#): > > Do mind elaborating a bit on that point, Mangetout? I’m curious. 🙂 > _props chin on hands_ I’m not a British pea, but what he means is that since black is the color of things that don’t emit (generally by reflection) any visible frecuencies in enough amount for us to detect them, a plant that used all of the light it receives would be like a sponge for light, it would absorb all light, reflect none and be black. Greedy little plant… _stares at her geraniums suspiciously_ ---
**Author:** ![Isilder](https://avatars.discourse-cdn.com/v4/letter/i/cc9497/32.png) [@Isilder](https://boards.straightdope.com/u/Isilder)\ **Post date:** [May 16, 2015, 11:23am UTC](https://boards.straightdope.com/t/1-if-its-a-plant-it-must-have-green-stuff-2-chlorophyll-system-with-biggest-bang-for-buck/719735/34 "2015-05-16T11:23:55Z")
> [@Mangetout](#): > > Ophiopogon is a good example: > [https://www.rhs.org.uk/plants/details?plantid=3636](https://www.rhs.org.uk/plants/details?plantid=3636) > > It’s black, but I dont think it’s any more photosynthetic as a result. It’s absorbing more visible light than some other green plants, but not necessarily making food with it. That site says that ‘Nigrescens’ is an evergreen… its actually an everblack… ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [July 15, 2015, 6:44pm UTC](https://boards.straightdope.com/t/1-if-its-a-plant-it-must-have-green-stuff-2-chlorophyll-system-with-biggest-bang-for-buck/719735/35 "2015-07-15T18:44:18Z")
Possible changed OP for SD UFO readers way back when (I didn’t see the early-Earth time frame)?: **If it’s a plant, it _must_ have purple stuff?..** > **[Early Earth Was Purple, Study Suggests](https://www.livescience.com/1398-early-earth-purple-study-suggests.html)** > > The planet might once have been dominated by microbes that used a molecule other than chlorophyll to harness Sun’s rays. Who needs chlorophyll when you have retinal? There seems to be a lot of interesting pro and con info here–not dispositive, of course. Any comments from our resident board of reviewers? ETA: strike “ **plant** ” above; insert…what? ---
**Author:** ![dracoi](https://avatars.discourse-cdn.com/v4/letter/d/90db22/32.png) [@dracoi](https://boards.straightdope.com/u/dracoi)\ **Post date:** [July 15, 2015, 7:01pm UTC](https://boards.straightdope.com/t/1-if-its-a-plant-it-must-have-green-stuff-2-chlorophyll-system-with-biggest-bang-for-buck/719735/36 "2015-07-15T19:01:17Z")
> [@Leo\_Bloom](#): > > ETA: strike “ **plant** ” above; insert…what? Photoautotroph, probably. [Previous page](https://boards.straightdope.com/t/1-if-its-a-plant-it-must-have-green-stuff-2-chlorophyll-system-with-biggest-bang-for-buck/719735.md?page=1)