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In February I received this flamingo flower, and the underside of some leaves has v-shaped brown patches. Initially, I kept it under a high-intensity energy-saving light bulb, and was wondering if this could have scorched the leaves. I don't remember if it came this way or it got the patches after the light. I've since placed it in another room.

one scorched leaf and some discolored ones upper side - discoloration barely shows

These photos were taken two months ago; since the plant is still alive and has sent up about two new leaves, I assume it's not life-threatening. The discoloration doesn't seem to have changed much. However, still out of curiosity, can anyone tell me what it's due to?

Edit Here are some more photos of the leaves, underside and overside (and they are recently taken): underside of leaves barely showing on upper side of leaf

  • added my diagnosis now you have new pictures – kevinsky May 3 '18 at 0:08
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It's really hard to say from the pictures. It could be:

  • over watering encourages fungus/virus/bacteria which will show as a dark spot with a yellow ring
  • physical burn from hot lights will also cause dark spots but they will eventually dry to a paper thin consistency

Now that you have added more pictures I can definitely say that this is a fungus/virus/bacteria. The last picture shows the classic dead spot in the middle with a partial ring representing new growth and the yellowing area around it representing the next growth stage.

These actors are always present in soil but only get a chance to invade plant tissue if there is a period of stress. Usually this is over watering but sometimes it is a reaction to the chlorine/fluoride in the water.

Most plants can outgrow the problem, as yours has. I recommend:

  • watch your watering habits and do not let the plant sit in water
  • consider the soil, how long has it been since it was re-potted? Perhaps you cut one third of the root ball off and top up the soil in the bottom of the pot with a free draining medium. These plants will do well with small bark chips in the mix to provide some drainage and slowly decomposing organic matter
  • Thanks - was wondering about that. It seems the discoloration starts at the underside of the leaf and possibly progresses to the other side, but it's not happening very fast at all. It also hasn't dried or crumbled - except one leaf you can see in the top picture, which I cut off. I'll add some more (and more recent) pictures in a day when the light is better. – Simon_Peterson Apr 30 '18 at 23:42
  • Added two better pictures now - hope they're more helpful. Comparing to the ones from 2-3 months back, it seems the discoloration hasn't really grown much. But it's strange... – Simon_Peterson May 2 '18 at 15:40
  • Thank you - to answer your questions, I haven't repotted it since I got it in February, and it's in a tiny 8cm (diameter) pot which it seems to have filled up. I've got some bark and other medium from an orchid which died (my bad); I'll disinfect it and try to do as you said about repotting. It would also help me find how the root system is doing, as the pot is not transprent. Should I cut off the leaves with spots on them? – Simon_Peterson May 3 '18 at 14:10
  • Also, do you have an explanation for why the fungus starts at the bottom of the leaf? And why it doesn't seem to take up the whole leaf, but rather a symmetrical V? I found these patterns interesting and wondered if there is some sort of natural/logical reason behind them. – Simon_Peterson May 3 '18 at 14:16
  • @Simon_Peterson Usually the fungus starts on older leaves. Why the V shape I don't know. Can you use filtered water? This would remove chlorine and fluoride as a potential problem. Also, take the plant out of the pot and look at the roots. white and firm is healthy, brown and soft is not. – kevinsky May 4 '18 at 1:30

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