I just started running a new 5th edition campaign and the druid (first time player) decided she'd check out plants wherever she goes now, having just acquired a herbalism kit. The table below should keep her busy for some time. Obviously, not every item of vegetation she comes across will be new and exciting, so I'll probably give a 1 in 10 chance of there actually being a cool new mushroom, flower, etc. in a given area. The chance will vary depending on the region itself, naturally. You can always just throw some funky fungi samples in a laboratory the party's passing through.
The table should be mostly system neutral, but DCs and the exhaustion mechanic come from the 5th edition. GM discretion and all that. Roll a d20 if you're scared of the more powerful stuff at low levels, but I recommend that you don't be.
d100 Random Plant Effects
Unless specified otherwise, determine duration by rolling a d4: (1) 1 minute (2) 10 minutes (3) 1 hour (4) 1 day.
1. No effect
2. No effect
3. No effect
4. No effect
5. Poison. Target suffers poisoned condition on failed DC 12 CON save
6. Target can understand and only speak the regional language
7. Heals d6 + CON hit points
8. Severe dehydration - suffer 1 level of exhaustion every 30 minutes until you drink 5 litres of water
9. Lightfoot - advantage on stealth checks to move silently
10. Antidote
11. All animals (incl. pets and animal companions) hate target
12. Poisonous unless cooked (DC 13 CON save, poisoned condition) in which case it provides a day's worth of nourishment
13. If boiled in d4 litres of water for 4 hours, the reduced liquid works as a potion of healing (enough for 2 doses). Loses 1d4 potency each day after the first
14. Gastritis, curable by any restoration spell or d6 days of bed rest. Target suffers 1 level of exhaustion after each day of activity whilst affected
15. Hot hands, capable of burning self and igniting flammable objects. d6 fire damage, touch
16. Target can walk on walls
17. Target can walk on walls and ceilings
18. Target experiences zero gravity
19. Skin colour changes for d6 days. Roll a d8. 1-7: rainbow colours; 8: invisibility but any held/worn objects are still visible (lasts d20 + 4 hours)
20. The extracted oils numb the body against pain for 2 rounds. The target ignores damage for the duration (even if reduced to 0 hit points). After the duration elapses, targets suffers from the accumulated damage plus bonus 1d10 psychic damage (only if damage sustained)
21. Polymorph into a random animal (roll on random animal table)
22. Eyes water uncontrollably for 3 rounds. Treat vision as lightly obscured
23. Descend through open space at feather speed
24. When burned, tastes like bacon. However, something will feel off about it
25. Polymorph into an intelligent regional creature (GM discretion)
26. Polymorph into the most recently touched animal
27. Polymorph into a random humanoid (roll on random humanoid table)
28. Polymorph into the most recently touched humanoid
29. True darkvision. Lasts 8 hours
30. The extracted oils numb the body against pain for 4 rounds. The target ignores damage for the duration (even if reduced to 0 hit points). After the duration elapses, target suffers from the accumulated damage plus bonus 2d10 psychic damage (only if damage sustained)
31. When ground into a paste with water, it can melt through up to 1 inch of non-adamantine metal when applied. One vial of paste can affect a surface area of up to 1 sq. foot (Note it is very difficult to effectively apply during combat)
32. Chewing gives resistance versus random damage type. Swallowing deals 3d8 poison damage (1/2 on a successful DC 15 CON save)
33. Vegetables taste like meat and vice-versa. Grains taste like lard. Lard tastes like blood
34. Savoury and sweet tastes are reversed
35. Anything consumed by the target is bland, but edible (poisons will still act as normal however)
36. All ingested poison is neutralised. Lasts 3 hours
37. If spat on by a diseased creature and then roasted, it cures that disease when consumed
38. Poison. Blind on failed DC 14 CON save
39. Makes skin hypersensitive
40. The extracted oils numb the body against pain for 6 rounds. The target ignores damage for the duration (even if reduced to 0 hit points). After the duration elapses, target suffers from the accumulated damage plus bonus 3d10 psychic damage (only if damage sustained)
41. Target's skin thickens. Resistance to piercing and slashing damage
42. Target moves at double speed for d4 rounds
43. Target sneezes whenever a random creature (roll on random creature table) is within 100ft
44. Plant glows whenever a random creature (roll on random creature table) is within 75ft
45. Can be used to prepare a herbal poultice. 12 hours of successful preparation required. Heals 1d4 hit points every hour for 6 hours. If the poultice isn't removed after 8 hours, there is a 15% chance of infection
46. Can be used to prepare a herbal poultice. 1 day of successful preparation required. Heals 1d6 hit points every hour for 6 hours. If the poultice isn't removed after 8 hours, there is a 15% chance of infection
47. Can be used to prepare a herbal poultice. 2 days of successful preparation required. Heals 1d8 + CON mod hit points every hour for 6 hours. If the poultice isn't removed after 8 hours, there is a 15% chance of infection
48. Plant screams when burned, deafening all creatures within a 20' radius on a failed DC 13 WIS save
49. Two creatures that consume this (1 each) are able to communicate telepathically across up to 100 miles. Lasts 1 day
50. Target becomes irresistable to men
51. Target becomes irresistable to women
52. All animals are friendly towards the target. Lasts 1 minute
53. All animals are friendly towards the target. They will become inconveniently so after d4 rounds. Lasts 6 rounds. The plant looks almost identical to #52
54. Target sheds its skin (there is new skin beneath), which is wearable by a creature of similar build
55. Target's bones turn to jelly
56. Target's Strength score increases by 5 for 1 minute. After the duration elapses, there is a 40% chance of muscles tearing
57. Target's Dexterity score increases by 5 for 1 minute. After the duration elapses, target gains 2 levels of exhaustion
58. Closest NPC will be drawn to the location of the target
59. Shaped like a tuning fork, each prong resonates when close to the other. A consuming creature knows the location of the other prong for the duration
60. Masks target's scent
61. The distilled liquid of this plant makes metal extremely brittle. 1 vial can affect up to 1 sq. foot of metal
62. Induces vomiting when consumed
63. Target's sense of direction is reversed for d6 rounds
64. No effect
65. No effect
66. No effect
67. No effect
68. No effect
69. Tastes awful, yet is more-ish
70. No effect
71. No effect
72. No effect
73. No effect
74. No effect
75. No effect
76. Tastes like a good meal from the target's childhood. The wave of nostalgia overwhelms the target for d6 minutes
77. Antidote
78. Antidote
79. Functions as an antidote if steamed
80. The distilled liquid obtained from this induces amnesia when consumed. Condition lasts d6 days
81. Target can breathe underwater for 3 hours
82. Target can understand and verbally communicate with a random animal (roll on the random animal table). Lasts 30 minutes
83. Changes target's hair colour when consumed
84. Releases a cloud of spores upon impact. All creatures in a 15ft radius fall asleep on a failed DC 14 CON save
85. Target falls asleep on a failed DC 15 CON save. Regains 2d10 hit points if it sleeps for at least 1 hour
86. When simmered for 8 hours with the skin removed, the consuming target's body turns cold and their heartrate greatly decreases. Their condition is otherwise unchanged. Great for feigning death. Lasts d20 hours
87. Target drains and stores heat from external sources. This heat may then be released by touching another creature or object. Every time heat is stored, there is a 10% chance of internal combustion. Effect lasts d10 minutes, after which point internal combustion occurs
88. Target smells exquisite. People like them. Carnivorous creatures desire them. Lasts 4 hours
89. Target becomes incredibly imposing to others. Enemies will not attack target unless there is no other reasonable choice
90. Can be ground into a paste to make a strong glue. Sets and dries in 1 minute when in contact with air or water. Requires DC 20 STR check to break bond
91. Juice is highly acidic and difficult to safely obtain. Deals 3d10 acid damage
92. Target's skin glows in the dark for d8 hours
93. Every creature the target touches becomes covered in painful boils on a failed DC 13 CON save
94. Target is immune to and may (via touch) dispel any magic of d8th level or lower for d8 rounds
95. Target's body becomes wet and slippery, reducing friction to zero. Makes them harder to hit, among other things. Lasts d10 hours
96. Target gains d100 + 40 pounds
97. Target's body instantaneously converts all body fat into energy. All Strength, Dexterity and Intelligence rolls have a +5 bonus. Duration is d4 + 1 rounds or otherwise at GM's discretion (maybe the target has a lot of fat). Target then suffers 3 levels of exhaustion
98. Target's body sprouts a random, fully-functional, monstrous body part. Roll a d6 - 1: claw, 2: spiked tail, 3: spider legs, 4: tentacles, 5: wings, 6: third eye
99. Target immediately knows how to use whatever they are currently touching and what it is used for. 5% chance that this is a hallucination
100. For 1 year, intelligent creatures within a 20 mile radius at the time of consumption view the target as a god-like entity and will follow them without question
