Having seen the answer (and so not playing), I would actually say that Yoss is accurate in his assessment both that it is "alive" and that it does not breathe CO2. Keep asking.

It's a good confusing thing, that's for sure. Let me think of another question.

I'll give you a hint, most people wouldn't call it a "plant" in a vernacular sense, even though I said "yes" to that question.  (As often happens in 20 Q's, some questions are just not suited to the item chosen, so it's hard to answer them.)

is it to small for the average human to see?

I have also seen the answer.

It is not too small for the average human to see.

Questions & Answers:
1. Is it alive?  Debatable.  If I had to pick, I'd say "yes".
2. Is it tangible?  Yes.
3. Is it an object?  Yes.
4. Does it breathe?  Pretty sure not.
5. Is it a mineral?  No.
6. Is it larger than the average human?  No.
7. Is it real?  Yes.
8. Is it a plant?  Yes.
9. Is it smooth?  Yes.
10. Is it a flower?  Debatable.  If I had to pick, I'd say "no".
11. Is it a fungus?  No.
12. Is it able to "breathe" CO2?  Not that I'm aware.
13. Is it too small for the average human to see?  No.

Next time I'll use the scratchpad instead of a private line to hide my answer.

It would appear we are not solving this one?

Since I know the answer, I feel the need to advise you to look at the yes questions and try to focus there.

A smooth plant, clearly tangible, and existing in reality.  It is neither a fungus, nor is it a flower...   Yet it does not consume CO2, nor does it consume air.

Does it live under water?

Questions & Answers:
1. Is it alive?  Debatable.  If I had to pick, I'd say "yes".
2. Is it tangible?  Yes.
3. Is it an object?  Yes.
4. Does it breathe?  Pretty sure not.
5. Is it a mineral?  No.
6. Is it larger than the average human?  No.
7. Is it real?  Yes.
8. Is it a plant?  Yes.
9. Is it smooth?  Yes.
10. Is it a flower?  Debatable.  If I had to pick, I'd say "no".
11. Is it a fungus?  No.
12. Is it able to "breathe" CO2?  Not that I'm aware.
13. Is it too small for the average human to see?  No.
14. Does it live underwater?  No.

This is what I get for posting my answer in a private line.

Is it a cactus?

Questions & Answers:
1. Is it alive?  Debatable.  If I had to pick, I'd say "yes".
2. Is it tangible?  Yes.
3. Is it an object?  Yes.
4. Does it breathe?  Pretty sure not.
5. Is it a mineral?  No.
6. Is it larger than the average human?  No.
7. Is it real?  Yes.
8. Is it a plant?  Yes.
9. Is it smooth?  Yes.
10. Is it a flower?  Debatable.  If I had to pick, I'd say "no".
11. Is it a fungus?  No.
12. Is it able to "breathe" CO2?  Not that I'm aware.
13. Is it too small for the average human to see?  No.
14. Does it live underwater?  No.
15. Is it a cactus?  No.

In reply to Yoss (msg # 235):

Not so private, is it?

[OOC; Are we supposed to ask the answer question in a private message? Because I wasn't made aware-- Also, you know that no CO2, means no photosynthesize]
Is it a ghost plant (a.k.a. indian pipe/corpse plant/monotropa uniflora)?

I'm just going with the give up option...   I'll debate how right it is after the fact.

Aww, come now, it's not that bad is it?

Questions & Answers:
1. Is it alive?  Debatable.  If I had to pick, I'd say "yes".
2. Is it tangible?  Yes.
3. Is it an object?  Yes.
4. Does it breathe?  Pretty sure not.
5. Is it a mineral?  No.
6. Is it larger than the average human?  No.
7. Is it real?  Yes.
8. Is it a plant?  Yes.
9. Is it smooth?  Yes.
10. Is it a flower?  Debatable.  If I had to pick, I'd say "no".
11. Is it a fungus?  No.
12. Is it able to "breathe" CO2?  Not that I'm aware.
13. Is it too small for the average human to see?  No.
14. Does it live underwater?  No.
15. Is it a cactus?  No.
16. Is it a ghost plant?  No.
17. (Hint from Yoss) Is it real and commonplace?  Yes.

pretty sure I covered that when I asked the 'is it real' questions (thanks Lulu :p)

The questions asked have been missleading, unfortunately.

You could potentially try going back over the questions and clarify each one, but I honestly wouldn't...   when it comes to 20 questions sometimes people succeed at getting something nobody can guess.  You should feel good about it and declare a win, then we get to know what it was and go 'daarrn'

Is it in a symbiotic relationship?

Questions & Answers:
1. Is it alive?  Debatable.  If I had to pick, I'd say "yes".
2. Is it tangible?  Yes.
3. Is it an object?  Yes.
4. Does it breathe?  Pretty sure not.
5. Is it a mineral?  No.
6. Is it larger than the average human?  No.
7. Is it real?  Yes.
8. Is it a plant?  Yes.
9. Is it smooth?  Yes.
10. Is it a flower?  Debatable.  If I had to pick, I'd say "no".
11. Is it a fungus?  No.
12. Is it able to "breathe" CO2?  Not that I'm aware.
13. Is it too small for the average human to see?  No.
14. Does it live underwater?  No.
15. Is it a cactus?  No.
16. Is it a ghost plant?  No.
17. (Hint from Yoss) Is it real and commonplace?  Yes.
18. Is it in a symbiotic relationship?  No.

So, if it's commonplace that means that a lot of people know about it, and it's pretty easy to find, which also means it has been hiding under our noses the whole time, so I don't know? Is it a friggin' daisy?

Questions & Answers:
1. Is it alive?  Debatable.  If I had to pick, I'd say "yes".
2. Is it tangible?  Yes.
3. Is it an object?  Yes.
4. Does it breathe?  Pretty sure not.
5. Is it a mineral?  No.
6. Is it larger than the average human?  No.
7. Is it real?  Yes.
8. Is it a plant?  Yes.
9. Is it smooth?  Yes.
10. Is it a flower?  Debatable.  If I had to pick, I'd say "no".
11. Is it a fungus?  No.
12. Is it able to "breathe" CO2?  Not that I'm aware.
13. Is it too small for the average human to see?  No.
14. Does it live underwater?  No.
15. Is it a cactus?  No.
16. Is it a ghost plant?  No.
17. (Hint from Yoss) Is it real and commonplace?  Yes.
18. Is it in a symbiotic relationship?  No.
19. Is it a daisy?  No. It is not "debatable" that a daisy is a flower (Q10), so that can't be it.  However, it is "debatable" that a daisy is alive since the status of being picked and dying or being alive and growing is not specified (Q1).

Let me know when you're ready for another hint.  I do not think you're close enough to guess specific items yet.  Keep asking generic questions.